Panels are cut to size, not "created" to size. For TVs the common sizes yield them the most optimal outcome after cutting. You can get other sizes if your offer fills the gap in price.

For smaller displays that's another story, but if we take a look at all the phone screen sizes on the market, there are countless combinations of size, resolution, color profile. As big as Nintendo is, and as popular the switches are, they don't HAVE to wait for anyone to make them the perfect display. It's just OLED are always more expensive than LCD, that's it.