far as I know, all we know is that Jeep never offered it. But since they won't tell us why, it could be a mechanical reason, or it could be a "we don't think the customer needs this" type of reason.
But other owners have swapped them in and they seem to work just fine. Just as long as it's not an 87-90 which would be 21 spline input. Although a 2.5L owner could use that.