I think hawlucha is off a chicken or some bird that can't really fly. It can jump, and flap its wings to go farther, but just isn't able to stay airborne for a long time for a sky battle. Although it can learn fly, and carry a trainer around in the game which suggest that is should be able to fly well enough for skybattles.
My second theory is that being part fighting type would put it at a disadvantage to all the flying types.