[throwawayian]

Because in many countries writing down feedback creates a liability.

There are a lot of people not aware that their thoughts and feelings towards candidates constitute discrimination, and in the event of an employee or class action going to trial - written statements collected like you’ve suggested can easily create a view of systemic discrimination at any sufficiently large company.

Additionally the threshold and context for discrimination changes over time.

One day, you saying a candidate was too meek or reserved may be grounds for discrimination if they’re not in a customer or heavily-networking/presentation role.