Because this cliché has been so overused we now just expect someone evil to suddenly appear every time a mirrored medicine cabinet is closed in a horror movie. With this in mind, film-makers have resorted to subverting the cliché by using the same setup, but when the mirrored cabinet is closed nothing appears (ooh, how subversive). It’s often used as a softener before some other jump scare is trotted out shortly afterwards.
The only problem is, sadly, it’s now got to the point where even the subversion of the cliché is now cliché.
Cliché Annoyance Factor: