Hey, I won't argue that. Problem is, we've got no way of finding that reason, and I say that as someone who's been here for three years.

[The world has its share of mysteries. At this point, he's chosen to just roll with the punches. Fewer headaches in the long run.]

It's not just a challenge, though. Battling's the only way for most Pokémon to mature. Has to do with these things called levels. More battles mean more experienced gained and a stronger companion to top it all off.