The public slowly lost interest in "Modern Classical Composers" after the turn of the century.
There was a time long ago when the family would gather around on Saturday night and listen with enthusiasm to Toscanini's orchestra on the radio.
There's not a lot of excitment in today's concert scene (at least in America). I recently attended a Haydn concert here in Buffalo. The room was filled with very old people falling asleep during the pieces and the orchestra didn't seem very excited to be there either. Even though I'm obsessed with Classical music, I know I would've had a better time at the Slayer concert playing in town.
Most "serious music" venues do nothing to attract younger listeners.
To be fair, I understand that the orchestra in my city isn't payed as well as some and that they can't get away with sneaking in "new music" once and awhile. Of course, if this was my only exposure to Classical music, I'd have been pretty turned off to the whole thing.
Anyway, people still compose to this day, but a lot of the music is deemed "too difficult" for most people to understand and enjoy. There are many opinions on why this seems to be the case.
If you'd like to peep some modern composers:
Arvo Part (still living)
Alfred Schnittke (passed away in 1998)
Karlheinz Stockhausen (still living). He seems to be spending most of his time rereleasing all of his old recordings and compositions. He did a lot of far-out stuff in the 50s and subsequently influenced quite a few rock bands as well. He appears on the cover of the Beatles "Sgt. Pepper's Lonely Hearts Club Band."
Check out
KONTAKTE / CONTACTS (electronic music).
It may seem a little strange to you at first.
http://www.stockhausen.org/ (quite a few audio clips...lectures, MP3s)