These are the jokes that got him fired. Don Ohlmeyer was good friends with OJ, and it became an unwritten rule that OJ jokes were off the table.
Which is why Norm made them. Prime Norm was great. He leaned a little too hard in the old jokes in the fat years, but I figure new material isn't a priority when you're secretly dying.
Telling Norm to do something—or not to do it—would have the opposite effect. The reason his Bob Saget roasting was a bunch of innocent dad jokes was presumably because a stage manager told him, "get him good."
Conan O'Brien recently commented that in the wake of OJ's death, more people are talking about Norm MacDonald than they are OJ. Which really tells you what an epic masterclass comedian/troll Norm really was. We didn't know how much we'd needed him until after he was gone. Some of us Internet upstarts could have benefited from paying better attention.