The UUP didn't help themselves with their cosying up to the Tories a few years ago, memorably losing their only MP, a Labour supporter, who resigned in protest at the move and trounced their official candidate at the 2010 election!
Personally I haven't a lot of time for Mike Nesbitt: I remember watching him posing in the Civil Service bar up at Stormont a few years ago, in his days as a TV presenter, and I suppose partly because whenever I think of sports presenters turned politicans I can't (somewhat unfairly!) stop thinking of David Icke.
The obvious retort to complaints about the DUP/Sinn Fein domination of Ulster politics is: "well, present a credible alternative and get yourselves into government instead!"
I suppose the only real reason for their existence now is that they still poll reasonably well in PR elections and the upshot of a single Unionist party would be no choice for voters at the polls determined to vote Unionist.