I would definitely say it's the latency issue. If the speakers are within earshot of each other, the timing differences is likely to make it a bad experience more often than not. If you really want this feature, get a house-speaker system that supports it and have Spotify stream to that _one_.
I a bunch of Denon devices from smart speakers to a soundbar to two home theater receivers and many of them support HEOS which can do whole home streaming.
It sucks that you have to control it with a mobile app (I did write a PC app using Tk but that is not much better than a mobile app!). Also I have had a lot of devices fail either completely or partially (WiFi just went on my 7.1 receiver the other day, the same receiver is relegated to a (awesome) stereo because the HDMI port). The 5.1 receiver was a decontented ‘pandemic special’ with no HEOS.
But that said, the whole home audio is great and works with my jellyfin and Amazon Music and TuneIn and presumably spotify.