Given the cost of an LTE modem these days I wouldn't be surprised if they start coming with integrated mobile service as a "feature" to ensure the ads and surveillance data always flow.
Why would they ever add that? Mass market means every penny added to the BOM counts. I mean I wouldn’t be surprised if some manufacturer added that but I imagine 99% of people who buy “low cost” TV’s walk right through the WiFi onboard screen and connect to the internet. The number of people who go out of their way to keep the TV off the network has to be incredibly low.