A lot of his value is tied up in assets that aren’t liquid (real estate). Also he is probably not worth as much as he says.

But the main reason is that these “cheap crap” things you mention are probably vehicles for money laundering from foreign actors. The best example are the NFTs he was hawking for awhile. Costs next to nothing to make and foreign states can buy a ton of them to give him money without it being easy to detect. Even if it is detected it is still legal to buy silly NFTs, right? Certainly more so than a foreign government giving a candidate bags of cash for nothing.