Yeah in case of the beard trimmer it's because it uses quite a lot of power so you need a beefy adapter to run it. These often still use NiMH cells and trickle

Yeah in case of the beard trimmer it's because it uses quite a lot of power so you need a beefy adapter to run it. These often still use NiMH cells and trickle charge with 100mA or so. For a mouse this is all irrelevant because it uses so little power that it can easily be powered by a regular USB. Also, many bathrooms don't have sockets anyway. At least not nearby (and cooper is expensive too these days)