Matt Birchler, writing about Wear OS at Google I/O:

All of their examples were on round watch faces and I couldn’t stop thinking about how much wasted space all of these round watches have. The watch face can take advantage of the shape, but all apps look worse or have more blank space because of this shape.

I have no idea why Wear OS manufacturers haven’t figured out how impractical round faces are on smartwatches. They make sense on mechanical watches where the sweep of the minute and hour hands influences the form factor. But on a device that often displays text and lists, a rectangular face is much more sensible.