It seems that doing something similar for Black Panther just wasn’t working, but when Captain America: Civil War came along, Marvel realized it could do the Black Panther introduction there, which meant, as Nate Moore tells the Empire Film Podcast, Marvel could then follow it with a Black Panther movie that wouldn’t need to be an origin story and thus could avoid the problems the earlier scripts had been having.
The franchise had seen the introduction of Iron Man and the origin story movies for Thor and Captain America would have already been in production.
Back in 2010, Marvel would have been knee deep in origin stories for the Marvel Cinematic Universe.