I thought Civ 5 was popular and that's a turn-based game too.

X-COM:EU was hailed as the reviver of turn-based tactical gameplay, and it did it in a rather shoddy way.


The factor I'm tempted to think of in terms of appeal is patience.
It might be just me, but I feel that the younger gaming generation today is too impatient. Which is why the main audience for D:OS is probably a more mature one.

Unless otherwise specified, just an opinion or simple curiosity.