Some bitcoins are died because of the forgotten private keys or lost wallets, some of them died because their owner died and some of them will be never in the system because technicaly they are burned in the adresses like :
1BitcoinEaterAddressDontSendf59kuE
1CounterpartyXXXXXXXXXXXXXXXUWLpVr
1xxxxxxxxxxxxxxxxxxxxxxxxxy1kmdGr
1dot1xxxxx1sv1xxxxxxxxxxxxxwYqEEt
1See1xxxx1memo1xxxxxxxxxxxxxBuhPF
1BURNED4fBBJPNBUzytg6Q3HVj7uFGBxNE
Why people send bitcoins to the "burned" adresses? What is the philosophy behind it?
They were not really burned bitcoin because they still exist and it's not the same with the others where we used the term burn where we literally deleted the token existence.
I'm not aware of this kind of address, how do they know that it is already a lost bitcoin or the owner is already dead? do they know the identity of the users?
At some point we never know if maybe if they would know it's a lost bitcoin already they could confiscate that funds may be depending on the wallet. But for sure this lost bitcoin slightly adds strength to the market of bitcoin decreasing the supply in the market.