Well, biometric data has already been proven to be worth less than a password - because once it's compromised, that's it for life. You can't change your fingerprints.

But yes, pieces of plastic/paper don't require the user to have an expensive-yet-easily-lost doo-dad that is also hard to replace. Have your phone stolen? Now you have to wait not only until the banks do their bit, but also until the phone shops reopen so you can start buying things again. Not to mention that if you forget to charge your "money", you can no longer use your "money". It's also not an option for those in poverty, or for the plenty of people who don't have a phone, let alone a smartphone. "Dollars" come in a lot of forms that you can use at any point in life and in any state except perhaps severe mental illness. High-tech electronic-only money certainly does not.