These are not only the reasons fast, secure but there are some other reasons too that are low transaction fees, increasing value while fiat value do not change like Bitcoin value changes.
Increase value in fiat and bitcoin is different because of their usage globally. Fiat have a stable price because the usage is balanced and well performed unlike bitcoin which is more presently active in trading and investment and not as how usual currency works is.
Actually Im not with the point why people prefer bitcoin over fiat because of transaction fees. Majority does want bitcoin because of it's fiat value that is increasing over time.