All those Bitcoins are not dead at all. They are just lost somewhere in Blockchain locked on wallets and no one thief can hack them. I’m not sure about people’s philosophy towards “burning” BTC. Maybe in such a manner they reduce the number of coins.
You say it by yourself, wrongly, but you do. If these coins are not owned by anyone and no one can ever access them, then they're burned/gone forever.
no one thief can hack them.
Why do you name him "thief"? Thief is a person that steals from other people. Burnt coins are deliberately not owned by anyone. As for the "hack", blockchain isn't a server's database that you can DDoS and change values. Whether the coins are sitting on a burn address or not.