But you’re proving your own argument false. Alias wasn’t allowed to do whatever it wanted and it turned out the better for it. Hell, Bendis wanted it to star Jessica Drew at first. It’s those restrictions that feed creativity. So they couldn’t use Carol Danvers. So what? Trish works perfectly well, is another MU character that’s given a much better refit than she might have had otherwise and her presence doesn’t needlessly tread on the toes of an up-coming movies.
Do you really think this show would have been improved by what, Captain America wandering past at some point? Thor swooping in out of nowhere to save the day? It already has a host of other Marvel characters in there - any more and you unbalance the series and detract from its main character. It’s just needless fan-wankery that builds up this impenetrable lattice of continuity barring many people from getting into the story.
On a more practical point, it costs money. If you want, say, Scarlet Witch to turn up and get beaten up, you’ve still got to pay Elisabeth Olsen to turn up (and that’s even if she’s not too busy to do it), costume her, stretch the effects budget to match how her powers are depicted in the movies, get approval on all of that from the movie side, which takes time at every stage. All for something that would take away from Jessica’s story rather than add to it.