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.
It's probably around like the number said in the OP, but I know NiceHash lost a lot of bitcoins too when it got hacked.
If only people knew how to keep their coins in their own wallets then this wouldn't be a problem at all.