Because they don't. It's too much guesswork, and honestly pretty complicated. From the user perspective the TV would appear to go offline every now and then, so also somewhat easily detected.

It's much easier to just throw a $10 5G modem in there, pay the $2/year subscription fee for service, and extract data that way. Assuming a 5-10 year relevant lifespan of the TV, they'd throw $20-$30 on top of the sales price for the modem and 10 years of service.

The 5G modem could run completely independent of the wifi network, be a completely different circuit, and you'd never know it was there.

Except they don’t do that either. I’m not aware of any TV bundles a 5G modem. Are you?