This interestingly broadens the "who's doing best or worst at EDI and GLA - EK, EY or QR" discussion above. In the competition for long haul Far East etc traffic you always have to consider all the players, not just the ME3. AF, KL, BA etc are all in that market as are TK. Looks like TK blinked first which is hardly surprising given that Turkey is not as attractive a destination as it was (see other discussion above) plus, I must admit that I would feel less secure changing planes at IST than at some of the alternatives.
As an aside, I assume that EDI showered TK/EY/QR with incentives to start services. As someone with more than 30 years senior airline management, mostly on the commercial side, I think they got their tactics wrong. Better to have picked one player, probably EY, and got them to double daily as quickly as possible. Not so good for the spotters but much better connections for the passengers.