The saying goes:

"If you owe the bank $100, that's your problem. If you owe the bank $100 million, that's the bank's problem."

and comes from 1976 "As I see it: the autobiography of J. Paul Getty". There were no billionaires back then. When you owe a bank 20 Billion while being worth 260 you are still in the first category.

There were obviously billionaires back then. For example, J. Paul Getty was worth an estimated 6 billion when he died in 1976.

https://en.wikipedia.org/wiki/J._Paul_Getty

Wrong in this case.

Here the bank can reclaim what is owed via other means.

Having to find "other means" to reclaim is exactly what makes it the banks problem.

Do you think it's easy to get someone with access to billions of dollars (of your money) to do something they'd rather not? They can tie you up in the courts for years since they're basically equal powers: an $800 billion bank doesn't get better lawyers than a guy worth $1 billion. A bank vs someone with just a million dollars means the individual is at a major disadvantage as lawyer fees can easily exceed that amount in attritional lawfare.

Also, the reason the bank suddenly wants to reclaim that money might be that the wealth has vanished. If Tesla drops 99% for whatever reason, they will have a big problem getting their money back from stocks.

That's a great point: counterparty risk is a much bigger concern on a billion-dollar loan