Whenever I would go to a chamber music event or an orchestral performance there will generally be two sets of people there - the old school bougie folk and a handful of conservatory students - the casual audience member is far and few between. Orchestras will have a better chance getting an audience by performing pops or some program full of video game music.
Still, going to the symphony hall, being part of that scene, this might retain it's importance for the upper class / professionals, and this alone could be enough to continue to support more than a handful of orchestras around the United States.
* And the only reason I can is because I studied composition and theory at University.