Some IoT stuff already does[0]. According to the trusty people on the internet, you can remove these with your defrosters, and the SIM inside has unlimited data. Of course, approach this with proper scrutiny, but I honestly wouldn't be surprised since their entire business model is based on people not understanding how suction cups work.

[0]: https://barnacleparking.com/

There is little point when there is already a huge incentive for customers to connect their smart TV to the internet (ie the "smart" features).

However you do already see some devices include a sim card. Home "smart" meters for the south of England operate this way. I believe some cars do to.

There's enough operator deployed wifi around for that already in most countries, so they don't need it.