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.
I guess it also depends on the aircraft type too. BKK is unusual in that it seems to be the only flight to the Far East that leaves in the 0100-0300 departure bank that uses a 333. HAN, KUL, SIN, CGK, HKG, TPE, ICN and HND all seem to be 77W whilst MNL is a 359 and DPS a 789 today (although some of those routes also have additional flights in the 2000-2100 departure bank that use different aircraft).
If TK are short of a 333, then I’m guessing BKK will be the flight that gets hit. If they are short of a 77W then there are more flights to spread the disruption between - although it seems certain flights are being disrupted more than others (HAN and HKG seem to be delayed a lot). Perhaps TK look at the flights with the lowest loads.