Why is it counter intuitive?
/(?<!\d)\d{8}(?!\d)/, here (?<!\d) comes first, but called lookbehind, (?!\d) next, but called lookahead. All are counter intuitive.
What's the reason to name it this way?
It's counterintuitive because there is no consensus whether time goes from front to back or back to front and you simply has a different mindset.
In English we say "Leave the past behind", yet "past" is something that happens "before" (fore = front).