I'm more familiar with Soundcloud from the publishing side: I seldom listen, but that's the primary place where I share my music.
The point is, SC isn't built as a service that provides a sound library. Just compare how easy it is to publish a track on iTunes and on SC: there's this huge button in the top that calls you to upload something. iTunes is a shop, it's got everything (actually, it doesn't have a lot of tracks, but you can replace it with Beatport or Juno, doesn't really matter). Soundcloud, on the other hand, is more oriented toward releasing what's here and now. I've hidden and deleted my own tracks a lot of times: sometimes they were WIPs that I didn't want to release anyway, sometimes I decided to remove the track from public access so I can release it on a label later, and sometimes I just decided that a track sucks and should be ashamed of it.
Could it be that these tracks were hidden because of similar reasons? Or, may be, they were uploaded by users who didn't have the rights to these tracks in the first place?
The point is, SC isn't built as a service that provides a sound library. Just compare how easy it is to publish a track on iTunes and on SC: there's this huge button in the top that calls you to upload something. iTunes is a shop, it's got everything (actually, it doesn't have a lot of tracks, but you can replace it with Beatport or Juno, doesn't really matter). Soundcloud, on the other hand, is more oriented toward releasing what's here and now. I've hidden and deleted my own tracks a lot of times: sometimes they were WIPs that I didn't want to release anyway, sometimes I decided to remove the track from public access so I can release it on a label later, and sometimes I just decided that a track sucks and should be ashamed of it.
Could it be that these tracks were hidden because of similar reasons? Or, may be, they were uploaded by users who didn't have the rights to these tracks in the first place?