Personal example. I already have an nVidia Shield. It works out of the box, it's nice, and it already does everything I want. Even if I jailbroke my TV's smartness, then said TV's smartness probably still wouldn't work as well as the Shield. And if the Shield ever messes with me, I can just replace it with a Roku or AppleTV or Chromecast or whatever.
There's just no strong motivation to try to root my TV. I don't like my smart TV but I don't need to, because the smart parts can be "replaced" by any number of external devices. My point is that I suspect many would-be TV hackers are in the same happy situation.
And the respective TVs work without internet - the only possible attack vector (by the manufacturers) is if they start trying to connect to random unprotected wifi networks, or god forbid the Amazon Sidewalk network[0].
There's just no strong motivation to try to root my TV. I don't like my smart TV but I don't need to, because the smart parts can be "replaced" by any number of external devices. My point is that I suspect many would-be TV hackers are in the same happy situation.