Well, for starters, because nobody cares. But that never stopped Hollywood before. And so we wound up with a full 30 minutes of nothing but Wonka getting through some trust issues he developed as the result of his dad being Christopher Lee. You'd think that alone would explain it.
Similar thinking was behind Ron Howard's remake of How The Grinch Stole Christmas, which added some much-needed scenes of a small furry getting beaten.
It turns out that the Grinch used to live with the Whos, but they bullied him for being a weird green thing. He had a crush on a cute girl Who, cut himself shaving, and fled the town in embarrassment, which is the normal reaction to that sort of thing. There's an important lesson here, if not the one they intended: The Whos are the real assholes, so don't feel too bad for them.