They lose their insurance for other reasons, too. Their employer changes plans; they get dropped from full time to part time; they lose their job and don't immediately get another.

And switching insurance plans at almost any time can be very costly, even if you go straight to a new one, as all your deductibles and out-of-pocket limits get reset. And then you have to hit them again when the plan year starts again, almost certainly sooner than a year later.