Sure. But the bank isn't going to give random Joe a loan to buy a Monet. That's why all this is far-fetched. There are scenarios that could result in 20MM loans being suddenly called. People with little assets generally don't get those loans though.
It's doubly far-fetched to talk about loans to individuals for $20MM. If you're applying for a $20MM loan, you should have an accountant and your accountant should have told you to put this kind of thing in a corporation. You'll still lose a lot but it shouldn't bankrupt you personally.
Well, it depends on how wealthy you are and the jurisdiction you live in. Loans are not taxable income and if you would have to pay some sort of withholding tax on a dividend (if you would want to borrow against your illiquid shares for example), then it might make sense to take out a personal loan. A bank might also be more keen to give you a loan personally.
But yes, obviously not that common. Random Joe won't be getting these. Random Joe doesn't have $20m in assets either, though.
For example, let’s say I buy a Monet painting for X million and a bank is willing to give me a collateralised loan of up to 75% of the asset value. If a bank decides to sell that asset tomorrow (i.e. at a suboptimal time) they might not even get 75% of the value back.
Debt is a lever in business and some people make it big by leveraging big.