I find it's a fear of commitment based on the logic that what's "cool" or "erudite" is inherently fleeting. If you take yourself too seriously or invest too much in one facet of something you risk being left behind or worse losing your identity, which is vehemently defended as unique despite the fact that it is quantifiable to the level of elitism (creating a further layer of irony). And really their entire subculture is based on contradiction and irony inasmuch that they come together in an effort to fight conformity.
Early movements towards individualism were born of expression, creativity or experimentation. It didn't matter what everyone else did; you were doing what you thought was cool. Today, what's "cool" is dictated not by the individual, but is rather thought of as the opposite of what the masses are doing. Again, irony prevails.
I've also heard an argument that it's a defense mechanism against an ever-informed generation where people have a much easier time accessing knowledge once limited to a much smaller group. The frustration of blurred cultural and intellectual classes, created by information proliferation, led to the creation of a condescending attitude. Which fostered an over-arching sense of irony.
That is a lot of nostalgia for something that isn't true for the most part. Pretty much every subculture has its norms and always has, whether punks or hippies, etc...
Frankly the thing I find most amusing is the massive derision for hipsters in a thread that basically is celebrating conformity.