That’s one of the reasons this model has persisted as long as it has: labor discipline. Employer-based health insurance is a very effective tool at keeping workers bound to jobs that are increasingly miserable. It’s not like the employer is saving a ton of money, either, because they subsidize most of the cost of the benefit. What they are getting is compliance and increased productivity from a shrinking workforce.
A lot of structural issues start to make more sense when you realize that these institutions are actually set up to prevent labor mobility, solidarity, and entrepreneurship — and to encourage the preservation of existing capitalist formations.