Music labels publish the music on YT in exchange for ad revenue, they won't be happy if someone would download their music for free, and making music is expensive, google how much just a single drum mic costs and you need lot of them.
YT shares income from subscriptions with music labels? I didn't hear about this, and even if they shared the download must be paid much higher than a view because after downloading a person could potentially listen for a track hundred times in a row.