I am afraid you are underestimating this number by a lot. These schools are getting a lot of international students from countries (I will let you guess which ones) where prestige is absolute king and its either Harvard or bust. Nothing else really matters. But they can’t just apply SCEA to Harvard. They need a two tier safety net (in relative prestige terms) on the quest to get into Harvard. Penn is the first tier because of its high ED acceptance rate, and Chicago is the second tier safety net, for when they abandon Penn and jump for HYPS. If they fall, one of these nets catches them.
Prestige trumps everything for these students and they are not a minuscule number.