Why do HRs look for experienced professionals with mandatory IIT/IIM/BITS degree?

I understand it's a good filter for freshers, but if a candidate is already experienced (3+ years) and working in a reputed organization, why does a tier 1 college tag matter so much? Shouldn't you focus more on his career progression, relevant work experience, key chievements, accolades, etc.?

Lately, I'm seeing a lot of HR posts on LinkedIn asking for a mandatory tier 1 college degree. How does this make sense for experienced professionals?

Very curious to know the justification from HRs and other folks. Maybe I'm missing something...