Why Can't Major Avengers Villain Kang Be in an Avengers Movie?

http://legendsrevealed.com/entertainment/2016/09/14/which-major-avengers-villain-cannot-appear-in-avengers-films/

MOVIE URBAN LEGEND: Marvel cannot use Kang, one of the biggest Avengers villains, in their Avengers films.
Very few things in the world of pop culture are quite as confusing as the matter of who controls the production rights of various Marvel Comics characters, since Marvel has parceled out the rights to their characters to so many different studios over the years that it can be extremely complicated figuring out who owns what character and when said studio got control of said character. We have already addressed a few of these confusing rights issues in the case of whether Deadpool was part of Fox’s X-Men rights or whether the Incredible Hulk’s movie rights are fully owned by Marvel Studios. Today, though, we delve into one of the most surprising characters whose rights are not controlled by Marvel Studios, and thus off-limits for the Avengers films
avengers
– one of the Avengers’ earliest and greatest foes, Kang!