But because the writers needed to give you someone to root for

Moreover, because it went from adapting a British sitcom to making an American sitcom. The famous tweet goes something like: "A waiter spills soup on a businessman before a meeting with his boss. In the UK the show's about the waiter. In the US the show's about the businessman."

Same reason Steve Carell went from playing David Brent to playing Brick Tamland. We don't find a powerful sleazebag as funny as a powerful moron.

Not that there's much difference these days.