I've heard that the reason we (most of us) don't eat the locusts enumerated as kosher in the Torah is that we cannot identify them. That is, we don't know what type of locust is referred to by the Hebrew word naming each kosher type.
Some Jews, however, can identify them: they (Yemenite Jews, I believe, or some Yemenite Jews) have a tradition that identifies the kosher locust types.
Why don't we trust those Jews? Normally we say ed echad neeman b'isurin, that a Jew's identification of something as kosher suffices to allow another Jew to eat it. This case should fall under that rule: we don't know which locusts are the named-kosher ones, the Yemenite community identifies them for us, we should be able to eat them.
(I'd understand our reluctance if we had a tradition the contrary of the Yemenite tradition: "such-and-such locust is not the named-kosher one". Then of course we would not trust the Yemenite license. But our tradition is simply lacking; why not trust the ed echad, the Yemenite community?)