Why do certain guided trail rides allow riders to canter/gallop?

SOme places do allow that, but only if they have essed the riders abilities and have determined that they are good enough to take part in such a trail ride. In this case, its fine (I wouldn't want to spend hours just walking-boring!). If it was really people who had never ridden, I would say that that is very dangerous and stupid! Some new riders can't even stay on a horse at a trot, much less a gallop! But I doubt that this is the case.