As long as there is money to be made off of a remake (no matter how bad it is) there will always be a point.
Besides remakes are a LOT easier than coming up with a new idea...
Don’t you know the cycle now?
First they adapt a movie from the past generation to Broadway and then they make of movie of the musical.
With the success of The Producers, it is obvious. Casting will depend on whoever is popular at the moment (it is all about recasting famous roles with other famous faces).
And the remake doesn’t have to be a success on its own. It can actually be used to re-release the original version too and to generate a lot of press about both productions.