Did you ask him? Who's polls? I've seen polls that are all over the place on this issue. There's a reason why gay rights are shot down almost every time it goes to referendum. The tides are turning, but it's slow and last time I checked Colorado still leaned to the conservative side. And what about those other 4 guys? Are they not at all to blame for this just because they voted first?
http://www.one-colorado.org/news/republicans-block-civil-unions-bill-supported-by-72-of-coloradans/
A February 2011 poll by Public Policy Polling found that 72% of Colorado voters support legal recognition of gay and lesbian couples.
Additionally, a Greenberg Quinlan Rosner poll conducted in 2010 found support for civil unions across political parties and religious affiliations, including 61% of Republicans, 84% of independents, 70% of Catholics, 67% of Protestants, and 55% of “born again Christians.”
The others are also just GOP towing the leadership's line. This last one, however, ignored his direct family impact, ignored his constituents, ignored equal rights, ignored national public polling, and just went with what Reince Prebus told him to follow.
And we call these people "representatives"? Who are they representing? Certainly not the people that voted them in and pay their salaries and health care.