You know why: becaue he's a Republibot, maybe even a Campbell operative.
I wouldn't mind if we lost that district due to splitting the R vote. Given a choice between sending a message in a single special election in a "safe" Republican district, when we have a ~30 seat majority in the House, and sending a message in a general election, I'll take the former. Perhaps the fact that this race is occurring by itself will give the message greater clarity and resonance.