Because the company will file bankruptcy and nobody will get anything. Requiring insurance up front at least provides some coverage for liabilities.
It's why you can't legally drive without insurance. It's not for you or your car, nobody cares about that. It's for the other people and their property.
Nobody is talking about criminal wreckless driving.
We're talking about assurances that you're going to be able to cover damages if you rear-end a sedan and cause $8,000 in repairs. That's why you're required to drive with insurance coverage.
It's why you can't legally drive without insurance. It's not for you or your car, nobody cares about that. It's for the other people and their property.