I've heard people say that hot springs stimulate the body's ability to heal itself. If that is true for pokemon too, maybe it got started because of that? Unlike our own pokemon, wild pokemon can't just go to a pokemon centre if they are injured. Maybe they all started coming there to recover from any injuries. The injured pokemon wouldn't have the energy to fight each other, and any healthy pokemon wouldn't want to start any fights because then there'd be nothing to protect them if they'd ever get injured.

[Armin gets more and more excited as he speaks, thoughts slotting in place in a way that really seems to make sense to him. Though, will it make sense to Dipper too.]

If, uh, if that makes sense, I mean...