Comment by amiga386

Other than the meta-answer that the game designers made it that way, or that you may need to farm kills for something in future, there is also the Zerg Rush answer: some creatures are literally bred to swarm their enemies, that's how the hive has always survived before. It doesn't matter how outmatched they are, provided every needling damages you at least a little bit.

It's not unknown in human warfare either:

https://en.wikipedia.org/wiki/Human_wave_attack#Use

There's a similar human need to protect what is precious. Defending your family, defending your motherland. Cities being seiged by a superior opponent don't just abandon the city in cowardice, because they know the opponent will just gain ground and still come after them. They don't want to, they'd rather you stopped, but they have to defend their territories, even if it means their annihilation. If you win, everyone gets killed, ravaged, enslaved, ... If they only have sticks, and you have missiles and jets... they have to use sticks. Can you imagine how they feel?

But yes, you're probably thinking of RPGs where the enemies are preprogrammed with the same hostility no matter what the circumstances, even if you're a God-killer and they're defending 5 coins and half-eaten sandwich in their den.