Let's lay out the reasons why a "Nintendo Cinematic Universe" would be bad

Whenever Nintendo movies are discussed, there's almost always a discussion that arises that leads to people (mostly kids) saying that there should be a Marvel style "Nintendo Cinematic Universe", usually leading to a crossover Super Smash Bros. movie.

Most people seem to think that this would not be a good idea and should not be the direction taken with Nintendo movies. However, most of them don't actually say why they think it would be bad. They just say things like "Not everything needs to be Marvel."

So let's discuss some actual reasons why an "NCU" would be bad. Why do you think there shouldn't be one?

EDIT: Very interesting how on every single thread saying they want an NCU the comments are overwhelmingly against it, but a thread about why it would be bad is overwhelmingly in favor of it.