You don't need to have two entirely different yet similar weapons just for different warheads -- such weapons are generally designed to be able to accommodate different warhead types in the same airframe body.
There are a few reasons why they might buy both, but we can only speculate and the answers are probably not that interesting.
So the best thing to do is probably just to go "that's kind of weird" and move on imo, not worth spending the brainpower or thread space to speculate.
