Cryptocurrencies that are transparent to government tracking are also transparent to whatever criminals want to beat you up and take everything from you.
Your usual non-crypto millinare likely have less money to steal on them than average grandma. Fiat millionare likely have two credit cards and $100 in a pocket. Or useless iPhone with Apple pay. So there is zero profit in trying to rob fiat millionare or billionare and tons of downsides.
And moving any amounts of transparent crypto over $100,000 just paints huge "rob me" target on your person.
https://xkcd.com/538/ I've never been so honoured to be able to link one of these.