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.
It doesnt exactly solve on-ramp / off-ramp, but it hides very well how much you actually have in total.
With nornal crypto you create direct track from a CEX to every place where you spend the money.