> There's no clean mechanism to control a fan's speed in-band on a normal AC wall switch.

There is.

I specifically purchased a Fanco Horizon DC fan as it has an optional physical wall switch which connected to the existing wiring for the fan it was replacing.

The caveat being if you use the wall remote, it's not compatible with the model with built in LED light fixture. This was a non issue for me as wanted to avoid any fan with built in LED light due to when the led panel fails, it'll be extremely difficult to replace vs having independent lights in the room.

I think most DC fans don't support wall remotes because it's cheaper and simpler not to, and provide a remote control instead. It's not a technical issue as you can absolutely find DC fans with wall controllers they are just harder to find.