Net worth ≠ has that money to spend. You can be worth Y amount yet have very little actual cash depending on the circumstances. Of course, you could also borrow the money depending on how much collateral you put up.
I understand it isn't the same, but when we're dealing with numbers that far beyond human comprehension I'm not sure it matters all that much any more.
Under normal circumstances, maybe, but this guy has made some mistakes lately that mean he’s pretty heavily leveraged and is under some heavy legal liabilities. He’s not as liquid as his valuation might suggest, and due to his liabilities, he doesn’t have the flexibility to just buy whatever he wants right now. Anyone paying attention to recent news can infer this about his financial disposition without knowing the specifics.
His shares of Tesla (660B), SpaceX (150B), Boring Co (7B) and Neuralink (5B) give him all the credit he needs. Plus he's got some good investor friends (as we saw in the Twitter purchase). He doesn't even need to liquidate any holdings.