It's not really a conspiracy theory. YouTube users can use royalty-free music, it stands to reason Spotify would have the same (potentially internally) to decrease costs.

"Why pay royalties if it's just going to be BGM for a massage parlor?" could be their reasoning.

I only go to massage parlors that display their ASCAP or BMI license in the window. I wouldn't be happy getting an ending if some musician is being ripped off.