It's because usually a proactive villain defines the conflict, and that conflict then defines the reactive hero.
You know, da jokah starts some shit and batman goes after him, an ancient evil awakens and yuusha must search for the mcguffin, aliens attack and humanity puts up a resistance. It's the antagonist that starts off by imposing themselves upon the world and setting the terms of... whatever it is is happening. So the aliens oughta be good. Guts is a great protagonist, but he wouldn't be who he is without the immense adversity he's forced to face, and most importantly without Griffith, one of the most reviled characters ever. There's a ton of examples where the antagonists are some cardboard cutouts that don't get fleshed out and nobody cares about them, but it's the endearing ones that make things dramatically more interesting.

Part of that could also be the recent (as in last decade) reaction to villains in popular media being wet noodles. They talk about how important a good villain is because nearly every big name movie and TV show nowadays has milquetoast forgettable villains barely qualifying as an antagonist.
Villains exist to give the heros contrast.

What is the question?

Whaaat? Who says hero's don't get talked about?