Well... we always have some Pokemon food that we get from the Monument. And a lot of the Pokemon born here aren't trained like we would at home. There's less fighting for them.

And not everyone trains a Pokemon for fighting. Some people just enjoy having them around to be members of the family, or for having them as a sort of therapy pet.

Really, most of them can fend for themselves in a lot of ways. Remember that while a lot of them are domesticated, they're still wild creatures. They may appreciate you as someone who brings them food, but the biggest thing to remember is that they do have their own personalities and not all of them are friendly.

... I've known many Pokemon who simply prefer to act wild more than domesticated most of the time.