Because despite what crypto MLM shills claim their “market caps” are, there’s no way to turn any amount of Bitcoin into serious amounts of money like hundreds of millions of actual dollars. Any attempt to liquidate that sort of dollar value out of crypto will quickly show what a sham the whole pyramid scheme of inflated value is.
Tether volumes on Tron and Ethereum would suggest that perhaps you may be incorrect. Probably not hundreds of millions of dollars at once if you aren't working with legitimate OTC desks who can handle that size but even if you work with the more sketchy p2p types it is possible to do 7-8 figure transactions.
China had more than 50% of Bitcoin's hashing rate. Most of it probably was to launder CNY out of the country. I suspect there is still some underground mining despite the clampdown. The days of large scale mining seems to be over, though.