Well the coup was unlike any other previous coups. It was lousy, it was slow and it was brutal. From the first moment, it was very likely that they fail. As soon as the initial shock-wave is gone, it was more or less clear for everyone that these guys did this coup with no support from any major players in the parliament. As soon as the minority parties condemn the coup, which happened really soon after people realised that the tanks on Bosporus was not there for any security reason (many people thought there is a bomb or possible Paris-like bomb attack initially) but to make a coup.
It is also the first time in the history of Turkish republic that the Parliament is directly bombed.
Many people now suspect that this was a well staged theatre of Erdogan. Anyone who wants to do a coup knows that now it is Erdogan, that is the head player, although he is just the head of the republic. They did nothing against him, he, on the contrary, turned it into a PR stunt. He went to Istanbul first, called people to get on the streets, etc. Now he arrests anyone who just might have something against him, including those who helped him against the coup...
It was also very unacceptable that Erdo comes out and claims to be the head commander of the Military forces. This title was not used since the first president and it was not meant to be used as the chain of command in the military was already reinstated and he has no military history, unlike the first president who was the commander of the resistance against Ottoman empire and occupying forces in Turkey's independence war. So there is a certain number of people who thinks this was just huge theatrics to reinforce the "Authoritarian Sultanate" dreams of Erdo.