Why didn't Leslie Neilsen play Terence Stamp's role?

I'm not saying Terence Stamp was bad, I haven't even seen the movie yet so I can't really judge him, it's just that you'd think David Zucker would have casted Leslie Nielsen in this role anytime he needs an old guy: did Leslie Nielsen not like the script or something?

I call movies that are considered 'bad' hated movies.