Whats with all these remakes of old movies?

To me it seems like the remakes of old movies are insulting to the original. Such as Nightmare on Elm Street, Halloween, Friday the 13th, i heard theyre redoing dirty harry too. And the worst is they want to make a new godfather with a small portion of old unused screenplay written by mario puzo. I cant imagine that doing the series justice ( even though 3 was pretty bad itself). Does anyone have an idea why they remake so many movies? Is it just lack of creativity or what? Thank you for any answers