the thing is: most of the marvel movies, that you named, werent actually made by marvel.
as they sold the movie rights to big studios, they were not responsible for the bad movies tnat were made.
Every movie they made after getting back their movie rights was pretty damn good.
also, the Justice league movie is allready in the works, the question is when it will come out (DC President allready said they were making it). They are working on Scripts for a Wonder Woman and a Flash movie atm, Superman probably will be the first in this series of movies.
Im kinda concerned tho, that they will rush the JL movie. Somewhere they said they wanted to make it before the single character movies, which is just stupid.
It might be ok for the US, but i can guarantee you, that it will flop in europe, because we just dont have the following for all the superheros in the JL. Here, people know Superman, and Batman, from the movies.
But as we had our own comics with Asterix, Lucky luke, TinTin and so on, we didnt have the superhero comics back in the days, so they are not that popular to most guys.