That is the expected result of colleges that use varied (holistic) admission criteria. The admit rate will not be 100% for all applicants above a stat threshold because admission is holistic, as well as because admission decisions depend on the needs and applicant pool of a specific college. If the holistic colleges all give a boost to a common hook, then highly qualified applicants who have that hook/boost have a greater chance of acceptance than similarly qualified applicants who do not have the hook, leading to a greater chance of having multiple acceptances. A similar pattern occurs for other strong hooks. For example, an academically qualified top football recruit is likely to be admitted to nearly any top academic college with a Div 1/1A football team that he shows interest in attending – a greater chance of multiple acceptances than similarly qualified applicants without that hook.
Another less significant factor is that certain groups are more likely to apply to all Ivies RD (and not stop after getting accepted to 1st choice early) than others. The Harvard lawsuit OIR internal reports mentioned that both URMs and lower income students were more likely to apply RD. I’d expect that having application fee waivers is correlated with applying to all Ivies, which also occurs more often among URM applicants.