Numerous reasons why people should use Bitcoin have already been mentioned. So I think the next question would be: why should people use fiat?
I think that because of simplicity, the appeal of Fiat will be more or less popular, and one should take into account that the bitcoin user must have education.
Fiat is the currency used today. You certainly can not put aside bitcoin. Bitcoin is a novelty, so of course fiat is now superior to bitcoin. But as time progresses it will change.