Possibly silly thought from a non-engineer, but I don't understand why the standard for wireless audio transmission is BT and not simply Wi-Fi, energy consumption?
That is a large part of it. More processing power needed = size + power consumption. There's other low power wireless technologies, but bandwidth is very limited.
Another important aspect is (standardised) inter-device operability without the need for separate network infrastructure (access point/router). Devices like smartphones can act as an access point, but this means losing its own connection to the home's WiFi network and it consumes power.
There's low power WiFi (Wi-Fi HaLow/IEEE_802.11ah or the upcoming WiFi 6/IEEE_802.11ax) meant for connecting battery powered IoT devices, like sensors and doorbells. But that still relies on access points. Power saving in part happens due to Target Wake Timers, turning WiFi on and off periodically and polling/sending data in bursts. Continuous streaming of audio would defeat that or you'd need to use data buffering making it unfit for low-latency.
WISA could be a contender, power consumption is in the same ballpark as Bluetooth and is low latency. The WISA modules are still too big for portable applications though:
"Earbuds, headsets, and portable speakers aren’t in the mix yet, simply because the current shipping module that Summit Wireless Technologies, Inc. showed me isn’t small enough for those form factors, and its power consumption is still too high. The specified power requirements, however, are stated to be about the same as that of Bluetooth. So according to WiSA, those types of products remain a distinct possibility."
https://www.techhive.com/article/3378198/wisa-low-latency-wireless-multi-channel-audio-standard.html