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.
Anecdotally inside my house, phones generally get no/weak cell service but WiFi is accessible anywhere in the house.
Obviously they could include both, but if it were relying only on cellular, my washing machine quite possibly couldn't get a connection