Mississippi has a mandatory liability vehicle insurance law.
The problem is it is just not mandatory, or at least, realistically enforceable enough to make it mandatory.
It is one of the most frustrating problems that face law-abiding, responsible Mississippi motorists, who as part of their privilege of driving, purchase liability insurance to cover accidents that might be their fault. Insurance companies never wanted mandatory auto liability insurance (they would rather collect uninsured motorist premium from people who have insurance, naturally, and only insure low-risk drivers) and the insurance lobby is powerful in the Capitol.
Now comes the state Senate with a bill that would actually put some teeth in the law. The Senate has passed a bill requiring motorists to show proof of liability insurance before being allowed to purchase a car tag.