Dom, it's because the foreshadowing is so very subtle that it effectively comes out of nowhere, and comes across as bad or desperate storytelling. Once you've seen the movie, in later viewings you can pick up the clues. But they are so subtle that the first time through, they don't even register as clues to something being up. They are so tiny and spread out that they don't add up to anything until you've been shown the answer. That is not good storytelling.
I'm sure it's very possible that more significant moments were filmed, but then left out in the final cut. For someone who has already seen the movie, the concept for the character works better. But the jokey, flip way that they treated the reveal still grates. If it were played more straight, it would be much easier to accept.
