>>26571683“Sinnoh Folk Story 3”
There once were Pokémon that became very close to humans.
There once were humans and Pokémon that ate together at the same table.
It was a time when there existed no differences to distinguish the two.
If it's as intimate as this sounds, I doubt people would want to keep something as significant as their partner in a ball, if the bond was as strong as this implies. This could also mean that they were more than capable of getting a job, having their own home, and so on.
Evolution must've taken a weird turn and dumbed the pokemon species down, even though they're much stronger, humans took the advantage of encapsulating them.