[2022] How come mods can fix/improve issues like AI but the devs can't?

Forgive my ignorance, but I wonder why mods can fix/improve core game issues like AI but somehow the dev team is having so much trouble? Don't mean to be offensive or something but genuinely curious...

It's a more general question too, not only for RoN. How come for so many games, mods so easily fix issues or improve the game so much but the actual game itself doesn't do these things?

Is it cause the dev team is a limited number of ppl and mods are created by third-parties that might have more resources, time, and people?

Also, couldn't the devs just partner with whoever made the mods and implement them into the actual game? I never really understood this lol