Very Good Question. Maybe someone here can answer it.
It seems to me that a fragmentation warhead would not require super high accuracy, and would be easier to design.
The only reason I can think of going this route is to be able to attack enemy vehicles maneuvering for a kill near one of yours, so you could take out the bad guy without endangering your own bird. But that's only a guess. In any case, even with an inert kinetic warhead, the collision will generate lots of fragments, so I don't see what would be the advantage.