It allows him to be one of the safest junglers while also having a good clear time and somewhat decent ganks. And compared to a lot of other AD junglers he scales REALLY well since he has safety from being ranged and is naturally tanky.
i've seen graves do clears taking only a handful of autos from jungle monsters because he can kite and interupt autos. He has been a top tier jungler for a long time, and is currently considered the best in this patch, because he does everything well. Having the safety that his knockback gives him isnt something that Graves needs in his kit