A significant fraction of the population has a religious or moral objection to eating lard. A smaller but still substantial part of the population objects to tallow based on vegetarianism or the terrible environmental impact of cattle raising.
I googled it, some breakfast items (egg mcmuffin, panckages) and apple pie.
It's probably just a money saving feature. I'm already old (34) and I've only ever eaten the veggie oil McD's fries.