The initial thought about them I had is that there would be rare monsters with rare loot inside of there. Turns out, it's pretty much no different compared to outside but a lot more cramped, this also goes for the gathering nodes inside there.

Now, i'm not saying "straight up make it better to go in there rather than kill the monsters outside", i'm just asking for some type of incentive to even bother going in there. The only reason I see to ever go inside of a cave is if you saw something like a black/pure crystal in there. Also, not that i'm saying it should be a thing(nor do I want it to be), but it doesn't help that you can't fly in there, which only gives me less of a reason to bother with caves.