A sibling to my last reply states it best: coups are risky and if the opposition chose the wrong side they'd be the first to go in a large scale purge. The resulting political landscape would be significantly worse for everyone. If the plotters had managed to capture Erdogan early on in the attempt and one of the coup leaders went on national television to show Erdogan's dismembered head then maybe, maybe the opposition could have gone along without taking an unacceptable risk.