Billionaires are much more skeptical about their money than people think , and actually they have all right to do that since becoming a billionaire isn't hard , staying a billionaire is the hard thing and with cryptocurrencies fluctuation rates it won't suite them to be switching titles all the day (prices up : i'm a billionaire !! , prices down : oh i'm a millionaire again , prices up : never mind i'm  a billionaire again !! and so on .. ) .
These people might invest a bit of money in cryptos but i don't think that they'll put all what they have in it since it is too much risk to go through especially if they hard earned their fortune .