They didn't even need to look at word of mouth impact to see a material hit on their customer retention, in a sector where churn is costly. They went on a crusade to improve, and now find candidates for jobs are net promoters, and their customer acquisition cost via candidates is lower than normal advertising(!)
I think some of the big tech companies simply don't care about their reputation at either micro or macro level, and nobody wants to call out that kind of toxic behaviour as they're all "part of the club".
At an employer prior to that, I saw first hand how companies were able to get negative but true reviews taken down almost as soon as they were posted. There was high turnover at that place and a lot of people were truthful in their reviews of the company. The Glassdoor rating was far higher than they deserved until they went under.
Im short, I’m sure you think you’ve got a great work environment, but I’ve been burned by bullshit Glassdoor reviews and I doubt I’m the only one.