Most DSL lines are ADSL and have limited upload bandwidth. Even for me I have 25Mbps down/800kbps up. I run bittorrent and have it QOSed and limited to 400kbps up. Uploading just one album would take all day (but probably shorter if done at night) so someone wanting to upload a sizable music collection will probably take longer than most people have the patience for.
Now, you could prioritize what albums get uploaded but then you're back to curating your music (picking which songs get priority) and most people don't want to do that. If any of these companies are able to do a music service without needing to upload files then they win.
Now, you could prioritize what albums get uploaded but then you're back to curating your music (picking which songs get priority) and most people don't want to do that. If any of these companies are able to do a music service without needing to upload files then they win.