What Adult Swim has been doing of late is a rotational system for shows. They have a large back catalogue now, what with Aqua Teen, Robot Chicken, Harvey Birdman, Home Movies, Squidbillies, Metalocalypse, but they want to keep rotating shows around so the ones like, say, Lucy Daughter of the Devil, which only has one season, and others don't start to get repetitive in re-runs.
The Oblongs and Mission Hill fit into that, they can run them out for a couple of spins, cover five weeks, then move onto another show.
I'm with you guys that they are a lot of fun. I remember seeing them both years ago, although only through Adult Swim, not wherever they might have been before.