Are you kidding? 2019-2014= 5 years. They (Prayuth was asked to make a coup, he did not decide it by himself) imposed 5 years of autocracy before elections. On top of it, the constitution they made was de facto giving the Senate (appointed by the army and the old elite) the power to chose the PM. It's still the case for the next elections. The opposition needs 375 MPs/500 to govern (provided elections are not rigged).
I forgot another reason, which was, the succession, and that's why prayuth had been appointed army chief in 2010
"The pro-Abhisit establishment and the powers that be are hunkering down for the long haul and Prayuth is their man. He could be in power for another four years – crucial in Thai politics because of the road towards the succession. The confrontation between the Reds and the Yellows is going to continue."
https://www.dw.com/en/thailands-new-army-chief-takes-office/a-6066746