Below is my precise illustration of how the so-called shuffle feature is broken. This is not a problem of people simply not understanding "true randomness". The shuffle feature will keep playing your most popular tracks first and it will keep putting the least-popular tracks near the bottom of the list. This means that you will rarely hear your least-popular tracks unless you listen to the entire playlist all the way through.
I created a playlist of 99 popular rap songs. You should be able to access it here: spotify:user:12139360648:playlist:19bWMy5OSgPuCdQfGAsMwW
Then I went to Forgotify and grabbed the first track it came up with: spotify:track:50CQRXMGKilUaa00o8pyua (Carnaval de Guaranda by Eduardo Cadena)
Since that track came from Forgotify, we can safely assume that it has massively LESS popularity than all the tracks in my original playlist of 99 popular rap songs.
This means that there are now 100 total songs in the playlist.
I opened the playlist and began playing it with shuffle toggled on.
Then I went to the Play Queue screen and looked at the first 80 songs generated in the shuffled playlist. Carnaval de Guaranda was not in the list. If I played the last song in the Play Queue (thus forcing it to reload the remaining 20 songs in the list), Carnaval de Guaranda DID exist on the second page, near the end of the list.
I toggled shuffle off-and-on-again (thus forcing it to build a newly-shuffled Play Queue from the playlist).
Carnaval de Guaranda is not in the first page of results. It IS on the second page, near the end of the list.
I repeated this test 50 times – each time forcing Spotify to “reshuffle” the 100-song playlist.
My newly-chosen, purposely “unpopular” track (Carnaval de Guaranda) was never listed higher than 77th in the shuffled list. Out of 50 trials, Carnaval de Guaranda was presented, on average, at the 87th position in the shuffled list. That’s not random. And that’s not what most people think of when they talk about “shuffling”.
So what difference does this make, as long as the song does come up SOMEWHERE in the list?? Well, if you don’t listen to the entire playlist, all the way through, you’ll likely never hear Carnaval de Guaranda. And if this “unpopular” track is always shown near the end of the shuffled list, that means that significantly-more popular tracks will always be shown nearer the beginning of the shuffled list. So you'll be more likely to hear them during an "average" listening session.
People rightfully complain that Spotify’s “shuffle” algorithm stinks. If you have sizable playlists, you’re usually not going to listen to the entire playlist in one session. You’ll listen for a few hours to one playlist, then for a few hours to another, and then maybe back to the original. But when you go BACK to the original, you’re starting back at the beginning of a newly faux-shuffled list. So you end up hearing a much stronger concentration of the same songs – even when you have a very large playlist.
Even if you did listen to the entire playlist all the way through, do you always want to hear the “unpopular” tracks near the end of that session and the “popular” tracks near the beginning?? If you added it to your own playlist, it’s probably “popular” in your mind.