“The culture in the X department is terrible, everyone works 80 hours a week and is miserable”
“Night life is great at least, the grad students usually go out for student nights at blah blah after seminar”
“Underrated X program because at university Y, don’t be fooled we literally have 4 of the 5 top researchers in field Z”
Etc.
Any product or service will have occasional customers who are either unreasonable or have bad luck. If you have a lot of bad reviews, then as a prospective customer you want to see if all of them fall under the two categories or whether there is a pattern that is relevant to you.
It seems to me that a review database works fine even when all the reviews are bad, and the only regulation it really needs is an effort to prevent one single individual with a vendetta from overwhelming it.