Disengagement works because not everyone out there is trying to talk to everyone. If you change cultural norms such that every child should talk to strangers a lot, it'll be tiring to have to do this "disengagement" 10 times a day.
And the risk for this happening… Do you think it’s a big risk? These days, a lot of kids just engage with their smartphone instead.
I'm pretty boring in person but there are definitely times I know strangers are curious about me. And those tend to be times I really don't want attention.