You just said that if Marvel believed in digital and TPBs/GN' as a way to sell their books, they would have a line that focused on that, and THEY DO. You also never said anything about them having to be ongoings. But these ARE ongoing, I've read them, hell, I'm
subbed to them. I subbed during the first arc, and when the second arc started, i didn't have to sub again, my subscription carried over,
because it is an ongoing series. They are continuing stories, just like any other book Marvel sells, they have threads that continue from one arc to the next, they are just grouping issues together under the name of the arc. They also did a standalone GN for Squirrel Girl, which does tie into the continuity of the main series, and she is is one of the younger characters. As for why other books haven't gotten one? *shrugs* maybe the Squirrel Girl one was testing the waters, maybe it was something North himself pitched and not some new initiative, I don't think it matters much, but it does demonstrate Marvel had faith in at least that one book being able to sell a standalone GN, there may be others in the future.