I’m not sure I see the problem. Is there a reason you expect to be able to use the service for free and even ad free?
I might only listen to a few songs a week. Is it fair that I have to sit through ads when I try to listen to them on Spotify? I don’t really want to pay for a subscription, especially because I already pay for YouTube. Clearly paying the full subscription cost for Spotify isn’t worth it in my case.
Edit: Don’t mean to sound like a smart ass. But as you can see, you can basically swap Spotify for YouTube in your argument. Spotify is just more valuable to you, which is fine. That doesn’t mean you should get the other thing free. Just like I shouldn’t expect to get Spotify ad free.