Apparently, people like to discriminate. Where there are overt markers, there is still a chance that people fear the legality of their discrimination. And when you remove overt markers of discrimination, people look for subtle markers, and those exist, and then still end up discriminating.
End result, even fewer qualified members of the discriminated class gets hired.
Occams razor comes to mind.
If anonymization reduced the representation of certain demographics maybe it doesn't make discrimination worse, but rather you were wrong about which groups are discriminated against?
I honestly fail to how that could happen.
For example, if HR is throwing away all resumes that aren't from an Ivy League, then removing cities and schools from the resume can only help.
Resumes need to be filtered to remove age, race, gender, name, even what school someone went to. Then ideally the first filtering round of an interview is also completely anonymous, a take home test or a video interview with camera off and a voice filter in place. Heck modern AI tools could even be used to remove accents.
HR has biases, those biases need to be removed.
It only takes a few moments of thinking to realize these techniques are a better way to hire all around. Nothing good can come from someone in HR looking at a resume and thinking "oh that isn't a college I recognize, next candidate."