Perhaps it is out of fear of sounding like the music of the past, where fortspinnung was essential in musical structure. I'm not sure why fear of sounding like Bach or Beethoven would be so overwhelming, but perhaps that has to do with one of the precepts of modernism, that you have to come up with something new all the time--art as fashion show.
But that doesn't bother me too much. I couldn't sound like Bach if I tried! On the other hand, I really like the sensation of movement, of harmonic process.