The Rest is Noise

[Maury]

This is an interesting question that the OP raises. As a counterpoint I would mention that Bernard Shaw was complaining in the late 19th C on the infrequency of Beethoven symphonies played at English concerts vs Spohr and Mendelssohn. There is also a confoundment in using the late 18th C as the benchmark since there was a stylistic break between Baroque music and the Classical style only a few decades prior. So listeners in 1785 were hardly going to demand more Vivaldi and Buxtehude.

As for Schoenberg, I think one has to also credit his rather logical analysis of where musical style was heading, i.e, the steadily increasing use of chromaticism. The problem with serial theory was not knowable in advance but only with the practical results of composers using it. My own feeling is that in the event, serial harmony was the stumbling block of the 12 tone method much more than melody. One just has to look at Schoenberg's greatest students Berg and Webern to see that both dealt with serial harmony by evading it. Berg used quasi tonal tone rows and Webern used the most tenuous harmonies.

To get back to the main point, I think audiences always prefer the established comforts over the new. It's just that this is always a relative process. When there is  a lengthy list of old favorites, audiences don't look for new music. If there has been a recent stylistic break then they want to hear the ascendant style even if new.

[Double-A]

Isn't the innovation of public symphony concerts (and the establishment of suitable orchestras) an important factor in driving the process?  At any rate the traditional repertoire (i.e. pre-HIP) used to begin with Mozart and Haydn (with the exceptions of Bach and Handel), coinciding with the beginning of the tradition of public concerts and the establishment of orchestras.

About Schoenberg:  His analysis is very plausible but maybe his solution less so.  He seems to have overlooked (or not cared about) the crucial role tonal harmony plays in the construction of large forms.

[Maury]

Yes of course there must be both chickens and eggs. Without the business side of classical music (halls, trained musicians etc) it would be hard to get to the aesthetic side. And yes, regarding serialism,  radical solutions have a low probability of success. As I said the OP question was interesting, but on reflection I think it quite difficult to dislodge concert audience preferences of long time favorites.

We are fortunate that there is another avenue for the unsung composers, namely recordings. Since these can tap a worldwide audience they can be very viable as opposed to local concert audiences. On rare occasions they will provoke some interest in conductors, orchestra and opera houses etc. Without recordings would Korngold or Zemlinsky have begun returning to the concert hall? So supporting the recordings either by buying physical media or with streaming services is the best way to retrieve worthy neglected composers.

[Alan Howe]

For many of us the 'concert hall' is largely an irrelevance or at best an occasional indulgence - especially if we live a fair distance from the venues concerned. This has probably always been the case, although mitigated for the past few generations by broadcast services of various kinds. 

Recordings (however delivered) are the means by which most music is consumed and appreciated these days. It has been recordings which have fuelled the huge expansion of the repertoire - for which we must be extremely grateful as this is something the concert hall would never have achieved.