But how would that affect the currency? E.g. what if some of the
top wallets are lost wallets. Is that making bitcoins more stable, since the lost wallets are not cashed out?
Nope. The stability of bitcoin is determined by live supply and demand. Lost money is dead money, it doesn't go anywhere. In a way it has an effect, as it lowers the potential live supply.
Practically, you could generate a paper wallet, put it in a treasure chest and bury it on an island in the Pacific. If it is found two hundred years later, and bitcoin still exists, then that money will be there waiting for whoever has the code.
The money belonging to lost codes will keep waiting until the cryptography is cracked, or someone finds the code.