D-list celebrities (I'm being generous) compete to win something. I'm not sure what they win. An escape from irrelevance? It's sort of hosted by William Shatner, who reads pre-taped clips to setup challenges and introduce new contestants. And let me tell you, he earned all $500 he was paid to do it.
I'd never heard of 90% of the people involved, which makes it easier to point and laugh. Lance Armstrong is on it and (surprise) he's a toxic asshole. Andy Richter (who I liked back when he controlled the universe) is on it and he's also a bit of an ass.
In any case, it will now be my headcanon that the rejected stars aren't rescued and sent back to Earth, but are forced to die in a Martian cave. And that Shat knew the whole time.