My take is that early 2000's felt like the last gasp of the monoculture, and now, like so many fanbases, rock/guitar-based music is more of a niche thing that you go out of your way to be a fan of. I graduated in '99, so I don't know if my perspective is skewed because I'm old and wouldn't know what's universally hip these days anyway, but that's how I feel.