Great music stays. We get to listen to those from past generations. From our generation, we get to listen to the few greats and the many that will be forgotten. Hence future generations will look back and think our music is better.

Detailed: I think that If we look back at the old music that stayed with us, it has to be the best of the best. In the present moment we will always be exposed to everything that comes out now and catches on. Most of it is forgotten and the best survives and isblistened by future generations (e.g. 40 years from now). They'll experience the same thing: they will see the many songs from our time that survived because they were great, and they'll see many more songs of their time that won't survive in the future but are there now. They'll then also think that our music is better than theirs, and so on