Pet Theories:

1) It's relatively easy to fly back home and stay "Turkish" with cheap flights on Wizz Air, and WhatsApp chat groups.

2) Erdogan lifting Kemalist secular cap allowed religion to blossom which means any immigrants from his era are more likely to be wedded to their faith.

3) The Turkish economy improved to the point that the smart fraction types and the mid level types don't leave anymore. You either get the activist/artist types, or the dudes from "the back" who are poor and looking for the short cut to success via Germany.