It's partially the general UX of charging a watch. I find it easy to put my iPhone on a stand next to my bed every night, but for some reason I find it annoying to take off my watch and put it on the same stand. Both devices generally need the same amount of effort to charge but ones more of a burden.

Maybe I just want to do it less because I'm wearing it not carrying it in a pocket or having it sit next to me somewhere.