how does owner of companies ever even loose so much money that they become homeless in a financial crisis?

If the company is brokw, and that's where the owner's income comes from, he or she doesn't have income so can't pay their bills.

If the company has huge debts, then that's how it happens

That is simple. The business owner presumes that income will continue or continue increasing at the rate it has been. They buy a house based on that assumption and when the business slows they are not able to make the payments. The number one rule of rich people is to spend below your means.