That probably simplifies legal matters. On the other hand, I really have no idea how that stuff works.
I'm an attorney and I have very little idea how this stuff works. Copyright and intellectual property law is a complicated issue.
Bendis being a post-1980s contributor, presumably has a contract that specifies what royalties, etc., he gets from "Alias" and/or any adaptions of same.
On the other hand, Marvel has seen both silver and bronze age creators--including Stan Lee himself
--try and sue when stuff they created, or co-created, gets made into a movie or TV series.
With this in mind, I can easily envision both Bendis and Marvel not wanting to open up another legal can of worms if they don't have to.