I never met a person in my life that owns a smartwatch. The market share of smartwatches compared to smartphones and tablets must be minuscule. And people who own a smatwatch most likely own a smartphone too, so it shouldn't be a problem for them to have a Bitcoin wallet with them. I never used a smartwatch, but I'm pretty sure it's more convenient to do Bitcoin transactions from a bigger screen of a smartphone.

So, to answer your question, it doesn't seem to be very practical or relevant to the userbase, and as others pointed out, it's likely insecure.