Just because he has Amazon stocks of that value doesn't mean he can turn all of that into cash. Economics explained has a great video on the various types of billionaires [1], which uses Jeff directly as an example of the lowest class of billionaire.
Just because the wealth isn't immediately liquid doesn't mean it can't be used. People borrow against illiquid wealth as a rule rather than as an exception. I don't think this argument holds water.
[1]: https://www.youtube.com/watch?v=0MeRN7LE1LQ