Because one of the best things about wearing a smartwatch is that you can use it as a silent (vibrating) alarm that doesn't wake anyone else up.

I've heard some people say that newer AWs can last indefinitely if you charge only while in the shower. That could be good enough. But I still don't want to have to bring another charge cable with me every time I take a trip. One week is good. Two weeks is great. A month is amazing (partly because after the battery degrades for years, it will still be two weeks).