I think he's one of those guys with an "if it ain't broke, don't fix it" attitude.

Look at Jim Carrey and Adam Sandler. Why would they all of a sudden want to be taken seriously when they've made creers and bazillions of dollars out of playing 40 year old adolescents. I think Stiller is too smart for this. Then again, he comes from a showbiz family, so maybe he knows better.