Perhaps this thread is California-centric, but there were other rock musician "communities" after Tom Petty. The 1990's grunge bands hung out together and most of them knew (and still know) each other. The late 80's hair metal contingent in LA were a 'community'. Were they all concentrated in one canyon? No. But communities nonetheless.
I think the drift of younger people's tastes away from rock towards hip hop and urban style pop has more to do with declines in rock radio than anything else. Rock has become nichified, which is nothing new, as there are several niches of hip-hop music, and there were niches and subgenres in rock when it was still popular.
It's just that when you have a top genre, which is popular, it's going to get the ratings, even if it has subgenres. Look at that Lil' Nas cowboy song. What genre does that fit into? Yet it was a massive hit, because he's already a star.
Tastes have changed. Those of us who are rock people deal with it. Either go to the internet, or seek out an HD2 if there is one. Maybe your city has a rock station that plays a few tracks you still like. Radio never satisfied people 100% -- I remember people complaining about rock radio in the 1980's when it arguably was at its apex. Can't please everybody even when ratings are good and it's popular.