It is commonly known that the probability of surviving after slitting your wrists is much higher if you cut horizontally and that you should cut along the forearm to cut a longer portion of the artery and bleed quicker if you plan to commit suicide.

However, people are often depicted in movies slitting their wrists horizontally.

Is this done on purpose to increase the probability that somebody imitating the movie will survive for example, or is this just a mistake or a coincidence that a majority of movies follow this convention?