I'm not a Spotify expert so I'm not understanding why independents artist without labels "costs money to maintain support" that isn't already spent to enable the labels to upload their artists' songs.
Let's say a Universal Music Group[1] representative logs into Spotify's system to upload Justin Bieber's latest 4-minute song. (Spotify has spent money on their backend system to enable this upload workflow.)
Why does it cost more to Spotify to let the unknown-Joe-Blow-not-signed-to-a-label upload his 4-minute song?