I think it's a question of liquidity. If most of his wealth is in equities, he can't just sell $40 billion of TSLA without causing a huge price drop and losing voting power, etc. The way a lot of super wealthy people get liquidity is by getting loans against their less liquid assets. I think Elon did a combination of selling TSLA and getting loans to put together enough money to try to buy Twitter, IIRC.
Most of his worth isn't liquid. As i understand it, it is difficult for him to liquidate enough stock to buy Twitter.
Most of his wealth is not liquid, it’s his ownership of his companies. It doesn’t represent his pay.