That Rockwell didn`t have much impact on subsequent painters just shows that painting was becoming a minor art due to technological advance. Rockwell operated much like a modern filmmaker, holding auditions for models and having his staff construct sets and assemble props. If he`d been born a couple of generations later, he might well have become a movie director.
It turns out that George Lucas owns even more Rockwells than Spielberg does. Together, they are mounting an exhibit at the Smithsonian: "Telling Stories: Norman Rockwell From the Collections of George Lucas and Steven Spielberg."
If your followers include Spielberg and Lucas, your influence lives on.