IMO people who train Wing Chun and look at full contact tend to be in two camps. The first wants to get in the ring and have a tear up from the day they start training and the second has no initial interest but reaches a point in their training when they want to really test what they do beyond their usual class stuff. Unfortunately every clip that I've ever seen of supposed WC fighters in full contact is of the former group. Whilst these guys might train well when it gets pressurised everything goes out the window and they resort to poor grappling or swinging for the fences. The folks in the second group tend to look for increasing reality with training partners in private, work out what they need to refine and then realise that they no longer have a desire to get into a ring.
To prove the point, take a set of pads along to training and get beginners to hit them and see how many maintain strict form.