I clearly explained Guardians of the Galaxy.
Ant-Man only happened because Edgar Wright had the film in development since 2003, back when the property was at Artisan Entertainment. Wright pitched the film to Marvel, not the other way around. It was a labor of love until he left the project due to creative differences.
And Marvel Studios doesn't let any director pitch anything anymore.
Trust me. Every choice Marvel makes serve a direct purpose. Feige has said as much interviews. They have a clear priority list and strategic vision.
And I agree they could easily. The question you should ask yourself is,
"Why don't they?"
Speaking of Inhumans, Marvel Studios even prevented Agents of SHIELD from messing with any of the classic Inhumans, since they had a planned film.
Drop Inhumans from the the film schedule and... wow!
Agents of SHIELD can use those characters now.