i think it's more the marketing
I think the marketing is a big part of it. Some instructors bill it as the be all, quick fix to self protection. Just like diet pills. If you'll notice, all of those diets say you need to eat right and exercise...duh!!!
Pressure points are a fine adjunct to a martial art, but as you pointed out, in an altercation your fine motor skills go out the window. However, if your gross motor skills are trained to strike in certain areas, as pre-set "one-steps" or similar drills do, you already have the pressure points hard wired in your brain.
With respect,
Mitch Saret