I don't get it either, and am free in saying 'no' if I"m otherwise busy or just don't feel like it because I am not the most social person. But if I have time and the dog is interested? Sure, go ahead. They're not going to jump on, poke, or scratch anyone. Mostly they're going to sit, get pet for a second and wander off (they're not exuberantly friendly, either). If it's a kid I kneel down with my dog (whichever one) to supervise more closely than the parents.
Also, frankly speaking, my dogs attend MANY performance events that people attend as spectators because the y're interested in the sport and/or the dogs. Having dogs there who can act as good ambassadors gives them a more positive experience, teaches them a thing or two, and increases the odds they'll show up in the future as competitors or will even jump in and volunteer at the event that's going on now (moving equipment, leash running, carrying score sheets to the secretary, in the ring setting bars - basic stuff). But mostly I think that being a welcoming committee at those events rather than being standoffish or rude is an important thing we do for the community. If my dogs don't want to be pet, sure, they won't be and i'll be the welcoming committee on my own - but if the dog is interested, the dog can participate in that, too, and add a little more to the positive impression. And, hey, if they don't I give a FRIENDLY 2 second educational blip on how you can tell the dog isn't into it right now and move on.
Dog sports are going to DIE if we keep being elite and holier than thou rather than welcoming new, even very green and not dogsavvy people, in .