Why put all the gear in a closet? Is it a requirement that the speakers be inside the walls or ceilings?

If powered speakers in each room (meaning not in the walls) is acceptable then the closet doesn't need to exist, for the audio stuff anyways.

My own audio gear per room has become simplified to (decent quality) powered speakers with a compact WiFi audio or Bluetooth box tucked behind or on top. Only thing going to the wall is a power cord. Very easy to move as the room gets redecorated and furniture changes or the room usage shifts.

I can imagine using an integrated amplified sound bar even when there is no TV in the room, if the sound bar fits with the decor demands.

I have reached the point where the only thing I run inside walls is ethernet cabling, to every room. And more than one per room. Cables can fail so some are for redundancy. Sometimes room functions change over time making it useful to have 'spare' network cables going to 'unallocated' walls and rooms.

Even with current mesh WiFi gear there are times where the better method is a wired connection. CAT5e (CAT6 now) can also carry HDMI or USB if needed.

My current house had in wall 'speaker' wiring running to multiple rooms along with in-wall 'volume controls'. And a centralized amplifier location. All of it has been abandoned/retired now.