Why are there so many remakes of successful movies?

I stumbled into the kitchen and a remake of “Arthur” was on. I’d never seen it, and wouldn’t have bothered with it, except that in this scene, there was the delicious Helen Mirren, and I thought I’d seen everything featuring her. Then up pops Nick Nolte. It took me a full 5 minutes to recognize the plot, but it set me to thinking: Why not try to remake some of the “dogs” instead of the winners?