Decentralisation also means responsibility.
You are referring to noncustodial, not decentralization. I mean noncustodial wallet.
Adding a passphrase to your wallet seed phrase it acts as extra security to the wallet. Many users did not care of this till now.
Yes, or going for multisig. But this has been discussed several times already on this forum after people know about the hack few days ago. I have seen people creating threads about it and using it to ask questions which will also have similar replies with this thread.