That is decentralized wallet I think hackers don't know your profile did not easily break your private key.
"Decentralized wallet". What does that even means?
What are you talking about?
Anyway, Hackers don't break keys,they steal them..
For sure he dont have any idea about the word "decentralized" which had been used into the sentence he do made

Is I am missing something or these online wallet do not provide private keys to users ?
Blockchain does provide phrases which do acts as a recovery when you lost up such wallet or simply a key that would used for you to access your wallet incase you lost it. These information shouldnt be shared out even into your family members

But the best suggestion is to stick with Wallet which you do have the full control like Electrum or Bitcoin core.