The state is told when cover stops
Insurers report cancellations electronically, and a registered vehicle without insurance can have its registration suspended. The notice goes to the address on file, which is unhelpful if you are away, and the consequences continue accruing while nobody is reading the mail.
Reinstating costs more than continuing
Getting a suspended registration back involves fees, proof of cover and sometimes a waiting period. Set against the premium that was missed, it is a poor trade, and it also leaves a lapse on your insurance record that affects pricing afterwards.
Traveling is when this happens
A household away for several months with mail piling up is the classic case. Autopay, a current address and telling us before you travel are the three things that prevent it, and all of them take minutes.