Yeah, recording techniques (and distribution of printed scores etc.) have a lot to do with the fact that people listen more to Beethoven than to Kurtag. In contrast to 1800, there simply is
a lot more truly great music available to all of us, so new music has a hard stance, since people can easily stick to their preferred style for their whole life without ever trying out anything else. Composers hadn't to compete with Bach in 1800, because there was almost no opportunity to hear a Bach piece, whereas today we compare every new piece with so many masterpieces we already know. So actually, the best way to make people listen to new music would be to destroy every score and recording that is older than 10 years
But jujimufu is right: There -is- an audience for new music. It's smaller than pop music audience, but it's significant enough. And we may often also be overestimating the size of the audiences the "great composers of the past" used to have. Even the "stars" of those times, even Handel or Rossini never had an audience comparable to the famous pop artists of today.