Often the worst companies put pressure on their employees to give fake positive surveys and pretend their company is a great place to work to trick people into a year or two while management moves on.
Seen it happen at a company that was voted top xx best places to work for a few years running in the local press.
I've seen HR at a major abuser massage Glassdoor rankings by disputing/threatening them with legal action for negative reviews and shilling/creating fake accounts to put in positive reviews. I believe Glassdoors policy is that they are not interested in lawsuits, so all it takes is a letter from a lawyer. Maybe even less than that.
Seen it happen at a company that was voted top xx best places to work for a few years running in the local press.