Because on the one hand, listening to spatial audio on headphones is fantastic -- I will absolutely never go back to regular stereo-through-headphones playback that sounds like comes from inside your head. Spatial audio feels like it comes from outside your head, and totally eliminates the "headphones fatigue" the inside-your-head sensation creates. And you can literally hear more detail in the music because there's more separation in the instruments.
But on the other hand, it's not super clear that spatial audio recordings are all that necessary for music, because the "Spatialize Stereo" setting works pretty well on its own. You don't need Dolby mastering -- my iPhone spatializes any stereo track already, doing whatever magic processing it does based on the relative volumes and delays of the same frequencies on the L/R channels.
I've tried listening to the same tracks using Apple Music's spatial masters, and in Spotify with the spatialized stereo version. The Apple Music versions feel maybe twice as "wide" with more separation between some instruments (and sounds are usually placed a bit differently). But on the other hand, it's not clear to me that that's actually a good thing. Because when I'm watching movies with my AirPods, I do want sounds from the left to feel like they're coming all the way from the left. But when I'm listening to music on the train or on a bus, too much spatial separation feels like it might be more distracting than desired. Spatialized stereo feels good enough to me -- I don't really see a huge benefit in remastering music in surround say, the way there has been a huge benefit in remastering movie audio from previous decades in surround.
But I guess we'll see. Especially with new speakers like the Sonos Era 300 [1] that are actually built to project spatial audio into a room -- so it's not just something for headphones anymore.