My point is the design was based around it's use as a phone. It wasn't designed as a camera or as a television - or it may have a different natural orientation. But it was originally designed to be held up to your ear, not to your eye.
Also, you mention "videos that are supposed to be viewed on landscape monitor." If you look at what YouTube, Facebook, and Instagram are heavily pushing, it's short videos in portrait orientation. Most cell phone videos only get viewed on cell phones or tablets, in portrait orientation.
So the design dictates the use, which influences expectations. Almost no one now finds it odd to watch a portrait-oriented video. That has an impact on photography, also. A half-frame camera produces a photo that naturally fills the entire screen most people are using (phone screen), the way people are using it.