It makes sense if online banks should hold a large portion of your wallet.

1. They give you interest on your money (which they can give to others for loans).
What if they start giving out bad loans to people who run away with the money. The bank will eventually end up going bankrupt and all our money will be drained.
2. Can protect & give you insurance if the wallet/password is hacked = all your life savings gone.
If the bank goes bankrupt then we will probably get nothing at all.
5. In case of fire or damage your hardware wallet (computer/phone/hard drive/USB stick/ back up) can all be lost.
Depends on how good we are at storing our keys. If a fire or natural calamity happens on the location of a bank then our money is lost anyway.
6. Option: If you forget your password/key, an Online Bank can help you recover your password/key and therefore all your hard earned money.
Storing backups is a good practice and in case we forget the password/seed/Keys the backups are the ones we look for.