The political situation in Thailand is very complex, and those seeking liberty a being crushed between old aristocrats in Bangkok clinging to royalist power and more recent looters elected by the peasants outside Bangkok, looters guilty of using their power to steal at least hundreds of millions while wrecking the economy.
The military has been on the sidelines (mostly) and the power battle complete with demonstrations has been going on since last year.
In showdowns in years past between the "reds" and "yellows" as the 2 groups are called, there have been bombs and firefights killing civilian bystanders. IMO, The military has patiently stood by in this year's showdown until the threat to innocents became too great. They gave both sides frequent warnings over the past 8 months. Up to now the military has been the only force that acted apparently in the best interests of the people of Thailand.
I am not close enough to the current situation to know what (behind the scenes) actually caused the coup and current curfew, but themilitary leaders likely understand the damage to the economy such an action creates. Western media reports rarely if ever give an accurate view with any understanding of the situation.