I think it is not burned, i think it was lost by users stupidity. But also how come people can send btc to a specified burn address. When in fact that address is already burned, the address is still active but not accessible? I'm a bit confused on what is really burned addresses. BTCBurn website got some concrete evidence that the address is really burned?
Some lost from users but there is the expression Proof of Burn that is an alternate consensus of Proof of Work and Proof of Stake. More details has the following wiki
https://en.bitcoin.it/wiki/Proof_of_burn. Even more there is an archived post in reddit with a list of these addresses
https://www.reddit.com/r/Buttcoin/comments/3kqdjv/a_list_of_bitcoin_addresses_used_to_intentionally/. Someone above told that people intentionally had burned their coins when exchange rate to fiat was low but I have neither read nor listen anything about it yet.