Evidently Robin Williams’ lengthy acting resume even at that time wasn’t enough to guarantee him a spot in the Harry Potter universe.
That should bode well for whoever she has in mind for young Albus Dumbledore in Fantastic Beasts and Where to Find Them 2.
While it’s hard to imagine anyone other than Coltrane playing Hagrid in the eight Harry Potter movies, it would have been fascinating to at least watch an audition tape of Williams channeling the half-giant.
If it’s any consolation, J.K. Rowling has said before that Coltrane was her first choice to play Hagrid, and her wish was granted.