People relying on desktop and software wallets. Storing them in their computers and eventually losing access to them either due to hardware or software failures.
Not just software wallets, but also things like 2FA. Many people either don't have back ups for their 2FA, or back up to another electronic device (such as phone and laptop). As OP says, if both are stolen, you can lose access to all your trading accounts (and web wallets if you are silly enough to use them).
Sensitive and financial information shouldn't be stored on computers.
On internet accessible computers, at least. It is perfectly reasonable to store your wallets on an airgapped computer, provided you take appropriate precautions to ensure the device is not infected with anything when setting it up, and securing it from physical attacks as well (whole drive encryption and storing it securely, for example).