A few key points with albums:
- You are listening to the artists vision/journey. The songs are not played in isolation but as part of a collective arrangement.
- Artists get payed more per play than individual songs.
- Albums don't degrade like playlists which can be changed by users or spotify to inject some newer commercial push.
I think this is less of the case nowadays. The latest albums I've listened to have all been just a complication of the artist's latest EPs with a couple of new tracks.
I don't know what is normal, but releasing singles or EPs before the full album seems like a common way to generate hype beforehand. Also, the Spotify model - assuming against what the previous comment says and every stream counts for the same revenue - doesn't differentiate between singles, EPs or albums, so it's whatever from that point of view. I've seen a few artists start releasing demos, songs-that-didn't-quite-make-it, and all kinds of unusual material that wasn't good enough for a full album onto streaming platforms, which then ends up in the long tail of their repertoire. It ties in with the article though, in that these songs will also start appearing in the playlists related to those artists.
Another interesting one is a single artist releasing songs under different names; Devin Townsend comes to mind, who can fill up a related playlist with songs released under his own name, Strapping Young Lad, Devin Townsend Band, Devin Townsend Project, Casualties of Cool, etc. And given he does many different genres, he'd appear - theoretically - on many different styles of playlists too, although I think the algorithm would get confused when the artist name gets associated with both hourlong ambient tracks and seven minute chaos metal genre mashups.
I think this arose in the radio-and-CD era of music. Maybe even earlier?
The radio stations that drove sales of new music wanted to play the latest releases. By releasing three singles before your 12-track album, you got more radio play, more shots at doing well in the sales charts, and hence raised your album sales.