What is the logic of having YoE (years of experience) ranges at companies for getting specific titles?

A particular unicorn's criteria for Senior PM is 6+ yrs of PM experience. I've seen extremely good PMs at 4 yrs of experience, and very bad ones at 8+. Why would a company benchmark titles at YoE?

I know it's to manage the feelings of others who have higher YoE - they might feel lesser, but why does a company even want people who are insecure about less YoE people coming at the same role - as long as they're judged to be of the same calibre as them?

Aren't such companies missing out on great young talent? Am I missing something?