Ilyana is only "pushed" on the x-men tittles, probably because the creators involved like her. Why Storm isn't pushed? Probably because Marvel notice that when she guest stars in a comic the sales don't rise, Logan is pushed because most likely the comics he is in get more sales. Simple.
I believe that aside from Wolverine, most X-Men characters would sell more or less the same on a solo, so the main factor on what character gets a solo is more about editorial and the right pitch.
Cyclops is my favorite character on Marvel, and I'm sure his solo would sell as well as Cable's or any other X-Men not called Wolverine, he have a rich and long history with connections to almost any x-villain, actually Sinister is more tied to Cyclops than to any other X-Men.
But Cyclops don't get a solo, if you ask me why, is probably because the x-office sees him more as a team character than a solo player, the same is true to most x-characters, so unless some creator comes with some good pitch for a Cyclops solo comic, he probably isn't getting one.