Beyond not disclosing the requirement up front being a clear dark pattern, I'd think this is self-defeating. The only time I need Glassdoor is when I'm contemplating changing jobs. Leaving a review for my current employer feels extremely risky, as the no. 1 type of users of Glassdoor are HR departments.
When I looked up an employer I’d joined recently, I gave a review as someone who had just started. Their most recent negative review was quite negative and easily traceable to the person who had most recently quit and was on their last days.
So reviews are either dishonest or not anonymous when they have to be recent; this pattern appears to incentivise some degree of pollution or self-incrimination.
The review I gave before leaving was much more informed and honest, in part because I timed it and in part because there were several people with my profile leaving at the same time.
