Hair dryers have killed people too, which are much more likely to be found in a bathroom. It's why they all have GFCIs in their plugs. I've also heard tell of a girl who was electrocuted in the bath by her phone charger. The USB cord won't do it; the 5V USB puts out can't hurt you. But if the charging brick and 110V wall power cord you've plugged it into falls into the water with you you're gonna do the 15 amp dance.

It really is to save those that aren't smarter than your average Bear from themselves. Logic would dictate that, yes, keep electronics or electrical appliances away from water, but too many people don't connect the dots. Also too, accidents happen to the best of us.