Some instead assert TVs might connect to the first open network available, like if a neighbor briefly opened a hotspot, which sounds more believable.
I think it's much more likely TVs make deals with cell phone companies and offer hardware that only works with their cellular service. Many pay more than $100 a month on their phone bill to pay off a phone. People might accept another $20 or so for a large screen TV with bundled apps-costs can be kept down for the carrier with ads and tracking that can't be bypasssed as it will use the carrier's network connection.