No one seems to know. I'm sure there are theories, but no real answers.

[Apparently there's a god pokemon around that might be involved. But he decided to not mention that. They had enough of gods and if it wasn't certain that it was involved, then he wasn't about to alarm Noel.]

Like I said, you can do more with them, especially if they want you to. Some are content with not fighting, but some want to fight apparently. That's where the battles come in. You can earn badges and challenge other trainers, if you wanted.