"I don't think there's an incentive large enough to get anyone from the Capitol to enter the arena willingly." So either they're not from the Capitol or this is some new kind of punishment that only includes certain of the Victors. Which raises the question: if they're not from the Capitol, then where are they from?

This is the strangest arena he's seen. Unusual creatures, a need to survive, but they've been given lodgings and the very environment isn't trying to kill them.

So there really are no answers at all.