TK is discontinuing comfort class on that route. It will be available on the outbound, no longer on the return. The last day you can fly comfort IST-IAH is July 27.
Because comfort class is going away at the end of July!
Comfort Class as a whole is not going away at the end of July. If it's going away on that specific route then it means they are putting one of the 9W leased planes on that route instead. There are several 77W destinations that do not have Comfort Class and never have (ICN is a good example). I'm more interested in where that plane is going to be reallocated to.