It's some extra effort to implement, so manufacturers might cheap out on it. For some devices it's considered a safety feature. e.g. an electric razor that's a

It's some extra effort to implement, so manufacturers might cheap out on it. For some devices it's considered a safety feature. e.g. an electric razor that's advertised as watertight and usable in the shower, because then someone will try using it in the shower while plugged in, and that's not a safe idea. Also applies to some medical stuff.