That's just how the Pokemon world works. One minute your riding your bicycle down route 17 as happy as can be, the next your chopping Arboks in half and melting Psyduck's into piles of goo on the ground. It's a wonderful world.
I would love Final Fantasy summons. But I doubt it would ever happen as most of the FF summons are based on actual religious deities. And Disney might not like having them in their game because of that.