Where are those billions now?
It seems to be another common misconception. People come to think that, for example, if the market cap shows Bitcoin capitalization of 100B dollars (an arbitrary number), then there are really 100B dollars invested in it. And even if they don't think so, many still think that dollars spent on Bitcoin (or any other cryptocurrency, for that matter) are still somehow sitting in the market and waiting to be exchanged for Bitcoin anew
This is not so for pretty obvious reasons. When someone sells coins and receives fiat, it doesn't in the least mean that he is going to buy back or buy in later. He may, but in most cases, the fiat money received by the seller is spent on something completely not related to crypto, and unless someone else (who receives these dollars in real life) decides to reinvest them in cryptoassets again, they are essentially lost for the cryptomarket