They could eventually use ethernet over HDMI or simply include a cellular modem of some sort. The profit is there.
But a simpler solution that we are already seeing a bit is to simply require a network connection to function at all; for now, it's just a periodic check, but a persistent connection requirement is all but inevitable in the medium term.
Devices having cellular modems isn't something new. Many cars already ship with them, for various purposes. WiFi will likely remain in use with smart TVs for a while as video content is data intensive so not really well suited for cellular, but likely stuff like your dishwasher or your stove might include cellular modems in the near future. The data they transmit is limited and you make setup easier as you don't have to type in a WiFi password any more.
Carriers run IoT-specific networks[1], which are optimized for use cases such as telematics (low power consumption, low bandwidth usage, but high penetration and coverage). So it's entirely likely that your washing machine would be able to happily send along telematic data via the same carrier your cell phone can't even establish a connection to.
But a simpler solution that we are already seeing a bit is to simply require a network connection to function at all; for now, it's just a periodic check, but a persistent connection requirement is all but inevitable in the medium term.