A reader's answer to the question:
You can't be both cool and culturally conservative. Consequently, being uncool helps preserve their edge in channeling cultural resentment.
Every so often a certain manner of post will pop up on my Facebook wall, usually along the theme of how rebellious it is to show deference to symbols of American authority (e.g. "I know that NO ONE's going to repost this because it's so UNCOOL, but I'm going to say the pledge of allegiance/post pictures of flags/support the troops anyway!"). These are almost always posted by the people I grew up with, i.e. working-class, non-college educated white people from upstate New York. To the outsider, this level of ostensible cognitive dissonance seems almost comical; really, how exactly does one rebel by pledging allegiance to their own government? It makes perfect sense, however, when you believe that these traditional sources of authority, tradition, and general cultural touchstones that once spoke to everyone, at least everyone you knew in your own life, have been supplanted by something else.
Of course Republicans are uncool - that's the way they like it. "Coolness" is an ephemeral, ever-shifting state, and holding yourself out as the antithesis of that says that you stand for these traditional sources of authority that everyone else is abandoning in the relentless pursuit of keeping up with the chaos of cool. The GOP would lose one of their best advantages if they tried to keep up with cool, especially when you consider that the older folks that form their base are quite well aware, from their own personal experiences, that coolness will outpace you in life, no matter how hard you try to keep up with it.
Coolness is emotional? I think Conor P. Williams was much closer with "cutting edge". Republicans are uncool because they cling desperately to some 30-year-old ideal. Democrats are much cooler than Republicans, though they'll never officially be "cool", because they don't. Democrats have always been more willing to change their opinions in the face of new evidence. On gay rights or gay marriage, energy policy, environmental policy and immigration, Democrats have been at or close to the cutting edge for decades.
But that's not the only reason. Because of the perception that Democrats are the more cutting edge of the two parties, young people are more attracted to them. After all, young people are most (or only) familiar with the current state of affairs and science. And so there's a positive feedback loop, where young voters are more attracted to Democrats in the first place, and then Democrats have to stay sharp so as not to lose those young voters. Imagine how cool they'd be if young people voted.