User blog comment:Mark4518/X-Men’ Producer Would Love An ‘Avengers’ Movie Crossover/@comment-1895174-20130219133851/@comment-3317214-20130219231440

No, I haven't, and I imagined that would be the case (Well, with the exception of the Avengers). But that was only three years. I'm not saying that I want the amount of interconnection they have in modern age comics, in the films (I don't think it would work, if that was the approach). But if the films had some cameos and just one-line references to the other franchises, it would show the connection without concerning themselves with complicated crossover movies.

And to LoveWaffle's point, that's all about writing. Joss Whedon's writing was the reason the Avengers worked in handling a large cast. And the writing on the X-Men films wasn't as good in terms of handling the ensemble.