First of all, Bitcoin seems not to be used widely as a currency simply because there are not too many merchants accepting it and not because the fiat payment processors are somehow more efficient than Bitcoin.
Even if all stores were accepting Bitcoin, then it will receive its Bitcoin related revenue from Bitcoiners, and not the average person that is still using fiat. You know why? You first have to obtain Bitcoin through whatever way in order to start spending it. With fiat, you can spend it right away with zero fees. So tell me, why would a non Bitcoiner even consider taking the step to buy Bitcoin, and then spend it when he can purchase everything with fiat already? It's an unnecessary extra step that doesn't make sense.
Besides that, the monetary function of storing value is obviously standing in the way of the means of exchange function. Fiat is typically considered as a poor store of value overall, which gives it advantage over Bitcoin (if that could be called so at all, of course). The latter seems to be another reason for not using Bitcoin as a currency
Fiat is a horrible store of value, and I personally find that it shouldn't be seen as such where the value part does not make any sense as fiat currencies around the world only lose value. So yes, Bitcoin is the leader in this aspect, but I have already pointed out this feature to be more important in the coming years. People are looking to escape this slavery system. Bitcoin is perfect for that.
