Until regional elections is the most probable answer
It makes sense, of course, at least from the government's point of view; they will of course get a lot of PR, advertising and national pride out of it.
If the plane makes its first flight shortly before the elections, with a big event, to influence the electorate for the upcoming elections, it's a smart move.
For us weapons technology nerds, it is of course a curse to have to wait so long.
On the other hand, it gives TAI more time to better prepare for the launch, to take the physical and physiological pressure off the staff to keep them fit.
These people are also working overtime without end for this project.
What I am writing now is just my personal opinion, the AKP/MHP has the right to do so, if they had not pushed the arms industry in the last 10-15 years both through flat hierarchies (less bureaucracy) and subsidized, then we would still be handling ancient equipment today, and at the mercy of the goodwill of the West as far as arms imports are concerned.