Looking at Ayn Rand's own experience during the writing of Atlas Shrugged (1957), she was engaged in a relationship during the 1950s with Nathaniel Branden, whilst still being married to Frank O'Connor(Whom she married in 1929). The thing people forget when we idolize the works of great people is that they are still human like any of us. She was likely in the midst of justifying her infidelity to her husband, and why her relationship had gone sour. She remained married until he passed in 1979. I believe she did love him, I also believe her actions were wrong. Authors often use inflection to better write their stories, making them an extension of themselves. This is why you see poor relationships, infidelity, and single characters. Ayn Rand strikes me as someone who suffered through clinical narcissism. Something that I have also struggled with in my life. While I still believe firmly objectivism is a moral philosophy based on solid axioms, it isn't without amendments (or statements/viewpoints made by Rand as she further grew her philosophy). Her later works illustrate her personal growth.

"I consider marriage a very important institution, but it is important when and if two people have found the person with whom they wish to spend the rest of their lives — a question of which no man or woman can be automatically certain. When one is certain that one’s choice is final, then marriage is, of course, a desirable state. But this does not mean that any relationship based on less than total certainty is improper. I think the question of an affair or a marriage depends on the knowledge and the position of the two persons involved and should be left up to them. Either is moral, provided only that both parties take the relationship seriously and that it is based on values."
-Ayn Rand's Interview with Playboy

TLDR
Books are a reflection of an Author, at the time she was writing Atlas Shrugged Ayn Rand was experiencing personal struggles with her relationship, the book reflects this. She is human like the rest of us and she did grow and learn from her experiences for the better in my opinion.

I can only speak for myself, but I do think there is something to be found in that. I think we start with max potential as children and slowly get set on our courses through our choices and actions. Committing to one thing means letting other things & potential paths slip out of our realm of possibilities and the decision to get married and decision to have kids are both pretty big determining forks in a person's course. Especially if you really love and care about the one(s) you commit to share your life with and pour a part of yourself into, but even those who rushed in (following the "first-love = true love" and "baby bug" rationale of teenage hormones) and come to regret & resent their decisions, they still come at a cost and alter the course.

I'm a happily single 37 year old dude & I do feel like I'm on a good path for me, but I certainly don't think it's right for everyone (That just wouldn't be very sustainable now, would it?). On the contrary, I sincerely hope that the younger guys who look up to me a bit can see both the good and the bad sides of me, rather than assuming that it's all sunshine & roses walking alone. I think especially now the majority of folks who have grown up with access to so many brain-tickling things to disassociate from reality whenever it feels like it's just too much, there are more people out there than ever who never learned how to be alone and it could very easily drive a person crazy or nihilistic.

Nature and nurture just shaped me a little differently and I never could quite settle for the "normal" or popular things/beliefs. On the plus side, I've been more free to explore (both my inner and outer world), find and follow a creative hobby/skill in my own free time (time is a luxury that few can afford, but in that respect "I am the 1%"), and dive a little deeper into way more good books, articles, lectures, documentaries, and podcasts than would even be possible for someone married &/or with children. But the downside of that is that I have to actively & mindfully manage & balance my own issues and left versus right brains, have to take care of myself into old age even (or however long I'm here), and will almost certainly die alone but I have come to terms with that. My dad passed away at home (not in a nursing home) with his whole family surrounding his bed and speaking to him, but still he passed away alone slipping back into his mind well before "giving up the ghost" and it seems like maybe we all do, so I try to maintain the best relationship I can manage to find with my other side.

In summary, the trade off seems to be that committing to pouring of one's self into other people and things and child-rearing almost certainly diminishes one's rate & scope of future personal progress and growth but while someone who walks alone might be able to explore & improve themselves a little further, they also have to face the facts that the further you go & more different from "the norm" you grow, the harder it is to find like-minded folks & everything you've learned but failed to share with others in your life dies with you (so my everlong quest is to keep searching for wherever I might be able to best fit and matter enough to others to be able to share and pass on whatever I can of the good things I've found). The shamans, artists, dream-readers, visionaries, and other such folks who find or make their own paths alone still need the rest of the tribe as much as the tribe needs them to keep positive progress and innovation balanced and free-flowing. Just my perspective on it. It makes sense to me that the biggest movers & shakers might often be single or in failed marriages without kids because they have more freedom to find or make their own way with more focus & less distraction.

Yes there is that tendency in life generally, having a family has been described as 'taking hostages to fortune'.
It makes those of independent thinking keep a low profile

I was also puzzled by this when I read the book. I think it reflected the difficulty of being truly selfish (as a virtue) when a spouse is involved. The heroes are all single. Hank Rearden was married before he 'went Galt' but got divorced prior to disappearing. Similar for children. Only mention I recall of children is the one woman raising her children in the Gulch (Dagny meets her near the market).

Interesting question. I'd guess it was some reflection on her life(?) I don't really know, though.

If I weren't a family man I'd be living on a 100-foot yacht in the Bahamas right now...

I don't think Rand generally introduced any characters that were not needed for the story.

And I think it could be seen as a mixed message if the protagonists' philosophy was to live for yourself, and yet they had dedicated their lives solely to another person. I know Rand has insisted many times that marriage, for lack of a better term, is an "exception" to the rules against altruism. Do I believe one can pursue one's rational self interest and yet still be married? I would say yes, though as a bachelor myself (with no desire to change that situation) I might personally not fit that mold. But one could argue that a lifetime partnership is at least in some small sense "living your life for another person." I've never been able to separate the two in my mind.

I will fully confess that my own commitment to lifetime bachelorhood is at least partly a reflection of my own independent spirit, that I do not think in my case, that I could commit my life to another person. I could never see myself as a husband and father. And in that respect I see some of myself in people like Rearden and even Ellis Wyatt.

Pure coincidence.