Actually it comes down to lack of need or desire. UAF has a much greater need for ground attack capabilities than air defense. Up until this week’s rocket attacks Ukraine has been able to mostly retain control of its airspace. Hence the reason that Russia flys very few missions into Ukraine and instead relies on missiles and drone launched from well outside Ukrainian air space. Even the recent attacks on civilian targets proves this, with a greater than 50% shoot down rate for both drones and missiles.