That's BS on it's face. Most states don't allow it or they restrict it to big business and government agencies.

It's 11 states, covering roughly a third of the US population. There's a quite few more if you own significant numbers of vehicles. You can s/most/many/ if it makes you feel better.

    Most people's money isn't making a return greater than what insurance would cost them.

You wouldn't be making money on a self-insurance bond either. It's locked up with the state or in a surety account. You can also expect to pay a significant fraction of your regular insurance costs to maintain a surety bond.

    Second, this completely ignores my point about credit.

Credit lines expire when you die (say in an accident), they're not guaranteed to pay out the full amount at any particular time, and the courts probably shouldn't go around binding third parties to pay out on your behalf.

States' interest here is in guaranteeing that there will always be a minimum amount of money to compensate victims, regardless of what other financial shenanigans you have going on in your life. That's not a standard that lines of credit and investment accounts meet. Self-insurance is simply a terrible option for most consumers, so no one does it.