The objects of nerd culture went mainstream, but the nerds themselves did IMHO not. And because of the change that mainstream brought on their objects, nerds are losing their culture. People can like the same thing, but for different reasons. And this becomes a problem when people are not aware of other people's reason and just start changing them, making them more matching their own reasons. So at some point, the traits that the original fans like are disappearing, getting replaces by the preferred traits of the new fans.
We've seen this many times. Star Trek being probably a very notable example, where the fancy new original Series was a great disappointment for many fans, while the (semi)comedy-version from a fan became the preferred love of this fans.
Well, TNG put the bar very high on quality. New series, don't.
On video games, even simple games like BSD trek and Super-Star-Trek on Python3 have great designs and still be played. The same with roguelikes like Nethack/Slashem.
We've seen this many times. Star Trek being probably a very notable example, where the fancy new original Series was a great disappointment for many fans, while the (semi)comedy-version from a fan became the preferred love of this fans.