Music, I'm curious.. how is this working for artists these days?

I don't understand this AT ALL... I have Apple Music... with very minor differences I understand that to be nearly exactly the same as Amazon Music, Spotify, and all the rest.. so we're all together on this.

I can listen to any song I want, at any time, (or nearly so)... and I think I pay around $15 a month for the privilege? First of all.. why would i ever buy music since I can play anything? I realize the artists are getting a 'cut' of my $15 but it really surprises me it equals, exceeds?, me having to buy an album, or song.

I have no idea how the 'download' thing works... if I can download anything? It seems so, but maybe not?

All of this makes most sense to you young people, , so I'm depending on you to explain it. Even though, this is curiosity and serves no practical purpose because I can listen to any song I choose at any time.