Lots of reasons. If you’re a gamer with a shiny new PS5 or Xbox then you’ll want the various updates for things like VRR and tweaks to the HDR performance. There are often other fixes and new features too that relate to image or audio quality.

I didn’t accept the various EULAs on my LG C1 TV. I’m able to update firmware but I don’t use any of its Apps. Instead I use an Apple TV for streaming and we don’t have a cable subscription. I haven’t checked how much data the LG is leaking (I really should turn off its Wi-Fi) and I trust Apple just enough to be less shady than LG.

TVs are more than just displays, and software has bugs. As an example, my last TV had numerous issues with CEC and HDCP [0]. this was _eventually_ resolved by a firmware update from Sony.

[0] https://www.sony.com/electronics/support/articles/00173195

BBC iPlayer stopped supporting don't older TVs. I think it was a codec issue, they only now support more modern codecs? In which case a firmware update might have provided a fix.

I know several older people who changed TV because of it.

But BBC iPlayer needs the internet to work.

If the premise is "do not connect it to a network to make it a dumb TV" then the apps that need the internet won't work anyway.

If the only thing is connected to is HDMI (and that device providers any apps you need)... Then surely firmware and software updates are not needed.

If course the key is to never ever give it any network or Bluetooth credentials.