[Akujin]

MP3s are so small compared to the rest of the internet now that there's a glut of shady websites that cater to people trying to get MP3s. Rings tones are a great example why someone with a Spotify account might google an mp3 for a song. Meanwhile you've got tons of semilegal mixes on Soundcloud and Mixcloud. Spotify and Apple Music is just convenience.

These sites also cater to the leaks scene. Every single hot album to drop recently was leaked 24-72 hours before dropping on "official" sources like Spotify. This makes even those people that have Spotify accounts look for MP3s.