I experienced this too. In fact it was within the first couple weeks of being hired that you were encouraged to post to Glassdoor (and a Linkedin post that they curated).

Definitely rubbed me the wrong way, but besides that they were really great people. I don't know if they realize what bad taste this is, just don't care, or if it's really just one person with too much influence creating policy.

This was a while ago, so I can only imagine it's become more prevalent. I've come to believe this is pretty much accepted behaviour for SV companies, and I wouldn't put much weight into Glassdoor reviews beyond just checking for red flags.