Estimates are estimates and estimated lost bitcoins are partially not lost bitcoins. We have already witnessed many old bitcoins woke up after around 10 inactive years.

Furthermore, with time and Bitcoin growth in adoption, value and price, I believe that the Bitcoin lost rate will become smaller with time. It's naturally as people will be more careful with their practice and minimize risk of losing bitcoins. Another thing is with higher price of bitcoin, people will be able to buy less bitcoin, fraction of bitcoin, so the lost bitcoins in the future will be considerably smaller than in the past.