When I first got my homepods they worked Just Fine® with Spotify; albeit I had to add to "hey siri" "on spotify", but it Just Worked® just like it STILL does in CarPlay. "Hey Siri, play Jamiroquai Virtual Insanity on spotify," "Now playing Jamiroquai--Virtual Insanity, on Spotify."
This is obviously NOT Spotify "refusing" to add a feature; it's Apple *crushing* competition, and moving to a completely anti-Steve-Jobsian *subscription* model of squeezing ever more money out of consumers.
I've been content to pay the Apple Tax for overpriced hardware for decades, in large part because the company culture was Respect For The Users. Apple Music is proving that credo has been tossed out the window. Reading the AM TOS I also see that Apple can track even your own CD plays and report them to the authorities--you know, just in case you didn't pay full retail price for your own CDs and additional subscription fees to Sony/BMG/WB/and of course AM. F'in'Hellen of Troy! What in gods' names happened to Apple?!? Just EVIL!®