Although that is one reason why people are allowed to pay a lot of money to do big game hunts. Often times it's an elderly male who isn't mating, but is preventing younger males from mating.

Yes.

Spoilers for every Monster Hunter plot:

The monsters in the wild are becoming way more aggressive/crazy, resulting in not only the ecosystem going out of whack, but also endangering human settlements.

You start off as a rookie hunter by culling them, and as you work up the ranks you discover that the source of this imbalance is actually due to a mysterious new monster (not actually that mysterious because it's usually the cover art monster).

You gradually gain more experience and kill the flagship monster, graduating low rank (the first half of the game), roll credits.

But it turns out the mysterious new monster only invaded the ecosystem because it was escaping from an even bigger threat, the new Elder Dragon of the game, whose awakening is a once in a 1000 year occurrence and is causing even more mayhem in the ecosystem.

You work up the ranks again, and slay the Elder Dragon, graduating high rank (second half of game), credits roll for second time.

Rinse and repeat for the G rank DLC/expansion, where you also get some new areas.

Canonically everything is done for the ecosystem. Gameplay wise there is significant dissonance as you genocide multiple species just for a 1% drop to upgrade your corpse dress.

yo what is that avatar?

This is one of the points covered several times in The Witcher series. The monsters are doing their thing, and should really only be messed with when they interfere with humans.

I started playing it but for some reason it's super badly optimized and makes my pretty good rig go potato mode :(

That's totally valid. No one's perfect.