There are also traders to wherever exchange they preferred to trade. Could be anywhere and they're actively trading top coin.
I was a day trader back in the days around year 2018-2019, although not rich like the OP mentioned, I can relate to some points in here aside from just "holding a Bitcoin".

In the harsh side, there could have been possibly a holder of Bitcoin that got locked out of their wallet as they did not remember their private key along with their password. I can hear the regrets.