The concept of the celebrity reality show does draw an audience, hence why so many of them last for several seasons.
However, most actual big name celebrities don't need the exposure, or would have such a huge price tag that they aren't feasible for studios to get. So they have to go celebrities who haven't done anything huge as of late.
King Koopa Not Going To Die; Childs, we're goin' out to give Blair the test. If he tries to make it back here and we're not with him... burn him.