but seriously, no one will admit they even have more than 10 bitcoin ...IRS/FED is the keyword 
That is not entirely true. Some people actually had the guts to expose themselves even though they were aware of the risks involved like:https://www.theguardian.com/technology/2018/jun/13/meet-erik-finman-the-teenage-bitcoin-millionaire
Most people though prefer to stay anonymous which is the preferred way indeed.