A post on Usenet made sense.
Fanboys and Fangirls pick up Emma Frost, Mystique, and Jubilee et al automatically just because they use x-men characters. But it was pointed out that while those first two books started out with good readership and then fell, similar x-books like Jubilee and Madrox won't get the same break. Fanboys and fangirls will buy anything with an X-character in it but most readers automatically put anything x on their pull lists, read them, then drop books like Mystique. Those readers are jaded and won't put the next swack of x-individuals on their pull list automatically, so Gambit et al are doing worse than expected. Thing is, even fanboys/girls have only so much money and they won't keep buying x-books for no reason unless their morons or completists.
Alpha Flight, on the other hand, brings in totally new readers to Marvel, around 5000-10000 at least. And books like Alpha Flight don't just take money from the same x-pie, they bring in new money, like Marvel Age books are trying to do. So to Marvel 10000 AF books sold is like 18000+ Nightcrawler books sold because Alpha Flight fans may not have bought Marvel before or anything Marvel but AF now. Quesada doesn't want those fans to leave Marvel so he wants to keep books like EXiles and Alpha Flight on the permanent list. I think Invaders was to be like that but unlike AF and EXiles I think Marvel overestimated its appeal to non-Marvel comic buyers.