Why are classical music supporters obsessed with symphonies?

I was just reading this New Republic article about the financial crisis in US symphony orchestras, and it reminded me of a question that I’ve had for a very long time: Why do people who enjoy  classical music lavish so much attention on gigantic symphony orchestras? Symphony orchestras have gotten polished to an extraordinary perfection, and suck up vast amounts of public and private subsidy, but chamber music performances are few and far between. There’s nothing in the nature of this musical tradition that requires emphasising the repertoire for huge ensembles. To put it differently, rock music would also be in crisis if it depended on putting together ensembles of around 100 musicians that would play to audiences of several thousand. Of course, there are a few bands that play to stadium crowds, but most of the professional activity in the most popular music genres is in small venues, with a handful of musicians and little or no support staff.

The same might be said of music in the schools. Most high schools manage to organise a school orchestra, but there’s rarely much effort put into chamber music. There, at least, the economics make sense, since dozens of children can be supervised by a single orchestra leader. On the other hand, the learning value is greatly reduced as well.