Niche culture is the very definition of cool. Yes if ordinary folk want to be cool then some of them will begin adopting the Niche culture. Once it's mass market it's no longer cool, inspite or even because so many people approve.
Any attempt to appeal to a bigger market immediately loses the cool factor.
Ordinary people are only pretending to be cool, they really just want to be like everyone else yet treated as if they are a little better than average.
Cool people are not even aware that they are cool, they do things for their own reasons and not anybody elses.
You can see the people trying to be cool, they pay more money for ripped jeans. Cool people have holes in their jeans that they don't care about because they are old and comfy.