Summary: Maybe the Judoon weren't the best choice when the Shadow Proclamation was establishing their police force.
As a sort of interplanetary police force, the Judoon leave a lot to be desired. Oh, they get things done, and they’re certainly intimidating to look at, but they’re not among the universe’s great thinkers. They can follow orders to the letter, but initiative isn’t their strong point. Let them make decisions on how to handle a situation, and you’ll regret it.
Earth is a proscribed planet, so to capture a plasmavore who’s taken refuge there, the Judoon have simply uprooted a hospital and dumped it in neutral territory, namely earth’s moon.