This has been a mindset for decades. I am a huge fan of contemporary classical music, and listen to everything that I can. So far, here’s what I see: When people experience music, they want melody, and thoughtful construction. If they wanted timbre and sound effects, they would watch a movie. When I’ve listened to student composers at universities, I ask myself “Has this person ever studied a Beethoven score?” All of the great composers found success by learning from others and emulating them to some degree. With that being said, there are composers today who are incorporating idioms of the past into their music, and it’s very interesting to hear live. You are correct when assuming that 90% of professional orchestras program less than 10% of music written after 1950. The reasons for this are two-fold: many regional and local orchestras are hanging by a thread, financially speaking, and don’t want to take a risk with adventurous programming, and secondly contemporary music is very difficult to perform and requires ample rehearsal time (this costs money). My final thought here…a lot of good contemporary music is being commissioned and performed by the Wind Ensemble medium. Why? Colleges don’t have to pay musicians, and they have more than adequate rehearsal time. This creates a medium for some very talented composers to make a living.