Why do Elon Musk, Mark Zuckerberg take out mortgages despite billions in wealth?

Why do Elon Musk, Mark Zuckerberg take out mortgages despite billions in wealth?
Musk, the richest man in the world having an asset value of more than $700 billion, recently got $61 million loans for five residential houses from Morgan Stanley. Zuckerberg, the seventh richest man in the world,...