I think we need to do some research here. How much of these lost Bitcoins is on the exchanges. As we know, Bitcoin wallets cannot be hacked by normal means. In my opinion there are very few hacking events due to the use of daily BTC.
Bitcoin currency is very safe so it is very difficult for criminals to break into bitcoin deposits, the possibility of missing is by going through several ways, one way that criminals often use is by cheating, giving promises that are very good and always offering big profits, but things like this are usually fraudulent, so the loss of bitcoin is caused by the owner's negligence.