It's Apple - they know more than you or I about their products and what their customers will buy, and they know how to market them.
That said, I think the screen is a tad small. My guess is that they felt the need to differentiate the HomeView with a smallish square screen in an effort to avoid comparisons to an iPad on a stand and to invite comparisons to the Apple Watch.
Version 2 will undoubtedly have a new larger screen launched with great fanfare.