Let's be straight about something here. Most of the routes that you reference lasted were test routes, Delta flew them for a year or two, or perhaps 2-3 seasons and dropped them if they did not perform. IST however is/was a route that they not only flew consistently since they got it from Pan Am. From 1991-1997 via FRA, since 1997 nonstop, and briefly at the turn of the century they also had a successful route ATL-IST as well (that went away after 9/11 and never came back). PAn Am had been flying the route since 1952 or so, so this is a route that essentially was intact for about 65 years, and that is a big difference than West African routes, or esoteric Eastern European routes that they played with for a short time. TK flying 14 times a day to the US, including ATL, sort of proves that there is demand between the countries. That being said, they might have pulled out after what has occurred over the last 6 weeks in IST, OTOH, the route lasted successfully through three prior coups and all sorts of other trouble over the years.
ABV
ACA
AMM
BKK
BSB
OTP
BUD
PUS
CAI
DXB
IST
KBP
ROB
BOM
VLC