>>28027658>>28027760>Only eats rocks.That's like saying a horse "only eats grass".
You'd have to feed your rock-pokemon a specific sort of rocks- you wouldn't just be able to shovel gravel into it's mouth and call it a day... Though keep in mind I wouldn't doubt that the Pokemon world would have Rock-Type Pokemon kibble/food/chow that you could buy in bulk or in huge bags or something to feed your pokemon.
While we're at it there'd also probably be people or towns who'd want to rent rock-pokemon to clear their work sites of rocks in the same way people IRL hire goats to mow lawns or keep weeds down via eating them.