Plus, people should really understand how someone being a billionaire works. They don't have billions of dollars sitting in a bank account somewhere.

They leverage their investments to take out short term loans or the like against their invested capital.

Musk is a billionaire on paper. Like most. His wealth is represented by his ownership shares of Tesla, speculation on the valuation of space x and solar city.

He's not selling his interests or shares in Tesla to buy things here. He's leveraging them.

Similar to how you can have your house paid off, and then get a new mortgage against your house for an injection of capital. You're leveraging the equity you have in your home. Which is based on the current perceived value of your home in the current market.

If the market changes drastically, so does the amount you can leaverage.

TL;DR; he does not have cash sitting around he can burn through to actually pay bills, and he's absolutely not going to pay his Google cloud hosting bill with his Tesla shares unless absolutely forced to (at which point he'd probably just sell Twitter).