I know people want "dumb" displays, but the reality is that these OLED panels offer industry-leading image quality and benefit from economies of scale, where most users want some form of built-in OS. A signage board cannot compete on price or quality. As long as TV manufacturers let me run it offline without issue, I'm fine with that.
Also fwiw, you can use apps like Infuse on the Apple TV for playing your own media files over the network. No Need for USB drives, just connect direct to the shared folder.