Limiting park entrance to only vaccinated individuals isn't how herd immunity works because those people are still out in the general population and exposed to the rest of the world all day, every day. Disney will lift masks and other restrictions when the general population reaches its necessary milestones, they're not going to try to gatekeep that at the park entrance.
Not to mention there are a thousand reasons people might choose to not be vaccinated that Disney won't want to adjudicate (children, nursing mothers, pregnant women, women who may become pregnant, religious objection, Qanon lunatic, etc.). Their lawyers wouldn't let them within 100 feet of that scheme even if Ops was inclined to try it.
WDW's restrictions are self-imposed and they will lift when public sentiment says they'll lift. It's not a scientific decision, it's a PR decision.