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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.
Personally, I treat my BTCs as an investment that I can always convert to cash whenever I need it or if the situation calls for such desperation. BTCs are too precious to be converted to cash due to their inflationary nature. Given that only a limited number of BTCs are in circulation, you can definitely expect that its price will continue to increase as time passes by.
I envisioned that my BTCs will work as if I own a business- where money moves daily (increase/decrease) without the need of doing anything in particular.