Because other top Power Forwards will almost certainly have higher JS/JR. If a PF has low OD, he is a basically a Center and will get torched on outside shots by his opponents. If you look at all the PF builds that people are suggesting, nearly all of them have a decent amount of JS/JR for their PFs, which is why OD is also needed. OD is one skill that you can almost never have too much of in my opinion.
Murray/Harris/MPJ/Grant/Jokic - 2020 NBA Champs