We all know why the 20 year rule is important, but it seems like modern political bias still leaks into events that are further into the past.

For instance, Ronald Reagan's presidency clears the 20 year rule easily, but it's still difficult to talk about his presidency with some people, because the bias is still very real.

So my question is why the 20 year rule is 20 years specifically, and not 30 years, or 35? Why is the line drawn here and not there?