But perhaps Coinbase (or some competitor, or some government) could offer such an insurance and that would be a valuable thing since it would make digital assets as safe as USD potentially.
And which is what I argue: They can't. It's much easier to steal, and it cannot be insured by a company that relies on those assets. This is not a bank. This is hard cash. Transactions irreversible. If a bank gets hacked, other banks can be informed and save the situation. Here
it is different.
Insurance companies insure very risky things all of the time. It potentially could cost a lot of money to insure, but it's certainly possible.
All things being equal, something secured by highly paid experts who have millions of dollars in resources and intense processes to help them should be far more secure than what any individual could possible come up with.
The endless list of hacks suggests that being a target is more significant than having a highly paid team of security experts.
Anybody with any significant amount of wealth is a target. The world we live in is not safe. That's just reality.