Finger foods are always more fun to eat, and eating has a HUGE psychological component.
It looks like more, is something novel and different.. they are easier to
eat.. smaller burgers like when we were kids hence triggering "happy kid" responses...
Often take longer to eat, therefore triggering our biological "full and happy" responses
while we still have food on the plate, which is a good thing to our caveman
hard wired memories.....
Oh, and they are prevalent in restaurants simply because they are in vogue at the moment. Enjoy them for they will go the way of the salad bar before too long....
sigh.....