Money come from investors and go to projects, or other investors. I've bought and sold ETH so many times, I think this question is so easy to answer.
A lot of money has been going to the USDT and back to the fiat form. So many people have been liquidating their portfolios to the fiatcurrency, bitcoin and stable crypto like USDT and i should suggest you to do deep research about this case and this is not easy as you said dude. It's not easy to answer this question because there was a lot of possibilities.