Cannot set HomePod minis as default for ATV-HD

I have everything running 15.3, my ATV-HD and two Home Pod minis. The minis are paired together and are in the same room as my ATV in the Home app - yet I still cannot assign my Minis to be the default speaker - the option isn't there!

I can manually set the output to my Minis, but when trying to set the DEFAULT audio to my minis, I *only* see "TV Speaker" - yet holding the Home button and selecting the AirPlay icon on the panel on the screen, my Minis CAN be selected. They'll stay selected until I reboot, a power cycle or if I redirect audio somewhere else, like to my AirPods.

When I cycle the power, I *never* see the setup screen, shown in the directions, asking me if I want my HomePod minis to be the default output.

What gives?