Tesla stock is immensely valuable but also extremely illiquid, because being seen to sell it off would tank its inflated price. So what he's looking for is a way to trade stock in Tesla for stock in something else that is less overvalued. This would allow him to sell back part of it and realize some gains. Otherwise, though on paper he's the richest guy in the world, he can't extract those riches as cash. If he buys Twitter in a stock swap, he can sell parts of it for actual money, which today he can't do without popping the bubble.