Decline of the gladius

[LegioIIavg]

I have been curious as to why the late roman army moved away from the gladius to a longer sword. I can understand that with a more cavalry centred mobile force the now more numerous mounted troops would need access to more longer swords to use from horseback but we constantly remark that one of the principle attributes of the gladius was its ability to be used efficiently at close quarters. Why then would the infantry give up what had been a very effect weapon for a weapon which, by its nature, utilized the edge of the blade more than the point, something that the romans used to mock their enemies for.

All I can come up with is that maybe those elements of the army that were barbarians and taken on en masse fought with their own weapons and that the majority of the army at this point in time were not romans per se. Any ideas ?.