Gen Zs like giving out mostly 3s, 4s, and 5s. A lot of satisfied kids who give 4s, kids who are really happy and give 5s, and a bunch of kids for whom the experience was OK. That would give you an average around 4. However, there are a small number who hated the school and give 1s and 2s, which will tend to pull down the average to around 3.5.
The average is irrelevant, because few objective criteria are being used. What is relevant is to see which things keep popping up and figuring out what that means to your kid. So Harvey Mudd has a large number of low reviews complaining about how difficult the classes were. That indicates that the academics are challenging, not that teaching is bad. A large number of people complain about how few parties there are. For some kids that is good, an for others it’s not. Important information, but the 1 that was given to it by a partier is meaningless.