I think the usual one is the combination of the the downside of failure (been to Chernobyl lately? Yeah, me neither) and the general feeling that there's no corporation out there trustworthy enough to not screw the pooch and walk away -- Bhopal anyone? One look at the kinds of indemnification demands being made in other countries where nuclear is (re-)emergent (like India) tells me that it's a non-starter: the reward couldn't *possibly* be worth the risk.
/jordan