"Watch battery life is measured in years."
Which means, when I had a watch, I was wearing it day and night. I'd hate having to take of my watch during the night to charge. While my smartphone somewhat automatically ends up on my desk during the day where there's a USB cable readily available to have it charged.

Interesting point being made by J Wynia, but I don't feel that as an issue myself. Otherwise I would be wearing a wristwatch today (which I haven't for many years).

Maybe the conclusion is: people who are wearing wristwatches today, _may_ be interested. The others definitely won't be.