Because storing encrypted online is both harder to do right and if your computer has malware on it then no amount of encryption will save you because at some po

Because storing encrypted online is both harder to do right and if your computer has malware on it then no amount of encryption will save you because at some point you will need to decrypt your keys. Not to mention that someone can still try to guess your encryption phrase. With a hardware wallet your private keys never touch your computer so they can't be stolen. Even if you are the kind of person that can't resist clicking on every piece of malware you encounter your Bitcoins can't be stolen from a hardware wallet. Bottom line hardware wallets are easy to get right.