Interesting, I assumed as much.
Annoying though. I leave my phone on my coffee table for hours, streaming podcasts to my Echo, a little music occasionally, controlling it with my Watch. I can pause it for ages, it will always resume when I press play on Watch, no messing with output dialogue boxes. Battery life loss is barely 20% at the most leaving it connected and using like this, and sometimes I leave it on the wireless Mophie charger anyway.
I know AirPlay is uncompressed and over WiFi but I’ll take the quality hit of Bluetooth for the convenience.
Should add, I don’t use Apple Music. HomePod would be an infinitely better proposition if I did. I simply don’t listen to music nearly enough to justify the sub though. 90% if my music listening is at the gym or running, the rest of the time it’s mostly podcasts.