It makes perfect sense to me. He is there to clean up the mess Jergal created in the first place. Those three had been nothing but trouble since he gave them the reigns.
He wasn't exactly trouble-less deity himself. All those godly domains were his. And gods wouldn't just "keep those domains on the shelf", so to say, Ao would never allow it. So, Strife, Death and Murder was very much how he influenced mortals himself, when he was in power.
He just grew tired of it, as no one really was able to oppose him for very-very long time. So, he very much just got a "retirement" position of a "dead scribe" instead.
There was bigger events, where those three wasn't involved at all. Like Spellplague (at time of which at very least Bhaal and Myrkul were still dead). And where Cyric was punished for it in the end (although not by Ao, but by other gods), Shar, despite being involved in it as well - never suffered consequences. Although she failed to became goddess of magic herself... she did however help Asmodeus still Azuth's godly power, and become god himself.
