There are thousands people lose their private keys every day. And it does not effect in Bitcoin value. Besides, those Bitcoin can not be used because no one know the private keys.
I wish there was some data regarding how many coins were lost this way but I think a lot of early investors and miners (at time when bitcoins was less than $10) might have lost their coins. I have read stories regarding how people lost the bitcoin details on their old system. Now, we are having additional storage options like physical wallet but there was no such information earlier.
Also, if there was some option to report these incidents and get the coins back. It would not have been hard to design in the beggining but the inventors may have not done this as a lot of people would have then tried to abuse this.