I saw the opposite at an employer. A bunch of salty people left and posted scathing reviews that were entirely unfounded. The employer encouraged people to leave honest reviews (they didn't pressure for positive, just honest) on Glassdoor, knowing it'd be nearly universally positive because it was a legitimately good place to work for everyone there (except the people that threw a tantrum and left).

Glassdoor refused to accept any of the new reviews. I assume they have some sort of mechanism in place to prevent a flood of new reviews, assuming it's something directed by the employer. Even years later I only see one or two new reviews despite dozens of them being submitted.