Hollywood loves a left-field casting choice. In an industry castigated for its lack of originality, the trick casting that defies prediction is still counted as a go-to chance for a delightful surprise. Which is precisely why Robin Williams playing a monster in One Hour Photo or Heath Ledger playing The Joker are so memorable. It's not just that they're great performances, it's that they come about so unexpectedly.
Even as they continue to pile identikit sequels onto the dung pile, Hollywood still shows a bit of a fetish for hiring people for jobs they have no right to be doing. If they work, the studios reap the benefits (and bask in the adulation of spotting something nobody else did), and you can see why they'd be so attracted to trying it every now and then.
But sometimes they go too far. It seems that the unexpected successes of casting against type have led to a culture of studios trying to force square pegs into round holes in the hope that they turn out to have been round all along. And when they don't work, the decisions look like the deranged machinations of severely warped minds, which is precisely what a significant number of castings for upcoming movies already look like.
They might work, but if they do it won't be because they're an easy fit...