because they will not know what to do when not working

go read up one a US asian millionaire .. inherit his fathers biz and grew it exponentially, for 20 years work hard until mid 40, never even married etc

one day, he just sold it off - try to start new biz but cannot huat like his previous biz, no excitement so he went las vegas gamble (one year, 20% of the casino profit all from him one)