Perhaps the musicians are acting according to their concience, based on their beliefs. That is a freedom that they have also.
Also, in case you don't know, spotify pays the musicians very poorly for the music that gets played on their streaming service. Spotify keeps most of the money that people spend on the service and the musicians who made the music get almost nothing for the use of their music.
I could care less about Joe Rogan and what he does with his podcast. I care that spotify takes advantage of the musician who put their music on spotify's streaming service. If they want to pull their music, for whatever reason, it is their right to do so.