What percent of people do you think are able to resist selling their BTC when confronted with huge profits they've obtained. Say 500% or more even?
Heres the problem:
Say you now have $20000000 equivilant in Bitcoin. There is no bank in the world that any sane person would trust that amount of money to.
The only sane thing to do is 1. buy gold or 2. (much easier) keep the bitcoin.
This is why most super wealthy bitcoin owners are not running to sell their bitcoin for bank money.
But you do not have to trust a bank. If you had this amount of money your best idea would be to diversify through different instruments:bank deposits, sovereign bonds, stock market, real business. Why would you risk holding all your wealth in one instrument instead? This is the riskiest scenario