My (sort of educated) guess: this is quite unfortunate, but when Operations folks need to delay any late night flight they will consider BKK first. Why? 2 reasons:

- the turnaround in BKK is long enough, so that the delay does not affect the inbound (BKK-IST) flight,
- the flight is short enough, so that crew will not go out of hours and their layover in BKK will not have to be extended (thus affecting the inbound flight).

(I am giving you feasible explanations and not trying to be on airline side - this OTP is scandalous.)

Please, however, have faith my fellow Flyertalker - I was on this flight some 7 weeks ago and we arrived into BKK some 15 minutes ahead of schedule.