But wouldn't he need to sell stock eventually to service the loan payments?
Or get sneaky and attempt other "creative" legally questionable solutions, like having an entity you control buy that debt from the bank and hold it while giving you a 0% rate, or something similar.
The bank doesn't just sit on those shares, they use them to generate money for themselves. For example, say the Bank takes $250M in Amazon shares from Bezos and loans him $1B. If the bank projects that the price of Amazon is going down, they short that $250M in shares.
If Bezos did need to pay off one bank, he just borrows from another.
Also, while it's called a loan, think of it more like a credit line.