Part of it is our age. In my 50's I don't laugh at the kind of humor I did in my teens. Maybe if the sequel came out a few years after the original it'd be funny.
I think it’s just that the original fire of genius isn’t there like it was at first. I don’t think that has to do with the age of the people involved, but just that things and people have moved on and changed.
I still enjoy lots of movies from my young days, but almost none of the sequels.
Maybe I’ll be surprised.