It's a choice between paying some interest, which has been quite low on loans, and paying the tax man. And yeah, these folks get loans easily because they have collateral which has a clear market value. Here is the difference:
Sell $20 million in stock, pay capital gains taxes of nearly $7 million Federal lon LT cap gains, plus whatever the state charges.
Borrow $20 million at 1% interest, pay $200,000 a year to carry the loan.
It's called margin borrowing, it's pretty easy to do. Very easy in fact, though I would be paying more like 6% at my loan size.
Meanwhile, you still own the stock which may well appreciate over time.