He doesn’t have $1 billion sitting in a checking account. If you tried to sell all the stock he had in Tesla, who would have the money to buy it? Nobody! Anybody who did have money to buy it would see the price go down due to a lack of buyers.
People don’t understand the difference between lazy and ambitious. Ambitious people create wealth. Lazy people consume wealth. That is the reason the hippie communes from the 1960s of all disappeared. The lazy outnumbered the ambitious and consumed all the wealth of the commune.