We paid for newspapers and they ran ads. We paid for cable TV and it had ads. We went to the cinema and watched ads.
Ad-free paid services were a brief aberration, essentially a bait-and-switch: "see how much nicer we are from the old-school competitors". Now that the competitors are gone, Netflix is doing ads, Amazon is doing ads... why wouldn't Spotify?
I hate it, but the reality is that we groan on online forums but don't actually leave.