… like 21:9. The shape of the wrist imposes a severe constraint on the height. So make the watch wide to compensate.
That way, you can see more information at once, like a map or a shopping list. Or an SMS, mail or tweet. Or a shopping list. Or a news summary. Or a game. Or many other things you can imagine. None of the above fit comfortably on today’s smartwatches, which are too cramped to be useful.
A smartwatch with a big, ultrawide screen will be far more useful, like a small phone, rather than just a notification mechanism or other accessory for your phone.
The screen space will also accommodate buttons for navigation, rather than unintuitive gestures like on Android Wear, where I had no clue which way to swipe and what would happen, or even what happened. Onscreen buttons also avoid the problem of unlabeled buttons on the Apple Watch.
Smartwatches would be an order of magnitude more useful and easy to use if they had an ultra aspect ratio like 21:9. They might even let some people leave their phones at home.