Board Thread:General Discussion/@comment-1031724-20160807010734/@comment-1031724-20160807013550

Because there is a wide variety of ways they can kill the villains, sometimes involving a spectacular light show, and three of them were destroyed by a different Infinity Stone (only one we've seen that didn't finish off a main villain is the Aether, which works differently than the others), and seems more a climactic ending.

Besides, none of the villains except Loki and Thanos are really popular, they're often considered to be lame, so they're all disposable, plus it's good to have variety and have a different villain for each one (Loki returned to be the villain of The Avengers, Thanos is likely going to be the villain of all Avengers titles, and Zemo is intended to return). I don't know, it just seems boring when they keep the same old villain around, unless it's Eggman (even some of the later Mario games are seeming a little repetitive, obviously for those who don't have older consoles).

But that was more of a side note that someone else brought up first, I'm just saying there's no way a 36-film series could stay as awesome as it is all the way through, but you're absolutely right I will continue to watch and love the old ones that I thought were good (especially Guardians of the Galaxy) if I find the later ones aren't.