Joking you say?! I never joke.
They're not needed since the compiler should be able to know all the types at compile. I remember years ago (2011?) Andreas said that for AS ver. 3.0 he wanted to revamp the language to allow this. There's a few options for this but it's not complete. There's no real reason other than simplifying the syntax for scripters to be closer to something more familiar like ZScript or CS.