Mike Lee and McDaniel are supporting Maness. I don’t know why he won’t drop out other than spite.
Maness probably figures that, if Cassidy wins big in the runoff, Maness will be forgiven for unintentionally (but negligently) running interference for Landrieu in the jungle primary, and he can run for the Senate again in 2016 if Vitter wins the governorship next year. (Why he thinks that it’s a good idea to make his first foray into politics a U.S. Senate run, instead of running for the state legislature or maybe the U.S. House, I have no idea, but unfortunately many supporters of self-announted “TEA Party leaders” seem to prefer candidates with no record on which to stand.)
Oh, and if he drops out he can’t use campaign money to travel across the state and run ads propping up his name ID (among other legal uses for federal campaign funds).