GlassDoor, in short, has become a textbook example of Goodhart's Law:
"When a measure becomes a target,
it ceases to be a good measure."[a]
The same phenomenon is known in some contexts as Campbell's Law: "The more any quantitative social indicator is
used for social decision-making, the more subject
it will be to corruption pressures and the more
apt it will be to distort and corrupt the social
processes it is intended to monitor."[b]
[a] https://en.wikipedia.org/wiki/Goodhart%27s_law