I wonder how new a phenomenon this really is. It's certainly been possible to get reviews taken down for many years.
Some time ago I worked for a company where I did a stint as a technical recruiter before moving into an interim head of IT role to tide them over whilst we hired someone permanent. One of the people I'd been instrumental in hiring whilst I was technical recruiter went on to join the company during my tenure IT.
It turned out that this person was not my - nor the company's - greatest ever hire. They were demanding, complaining, entitled and, above all, lazy. We bought this person a bunch of special equipment, including a ludicrously expensive keyboard supposed to help with RSI. Still, they continued to be obnoxious and lazy, literally doing nothing productive, until they were asked to leave during their probation period because they were basically insufferable.
Said person then went on to post a slanderously inaccurate review on Glassdoor about the company, their manager, and the people they'd been working with in that team. At this time I wasn't particularly happy at the company, for various reasons, but even so, I could see the review was completely unfair and, substantially, a work of embittered fiction.
I was pretty annoyed and felt somewhat responsible given that I'd been part of the team who'd brought them in to the company. So, with little hope of recourse, I contacted Glassdoor explaining the situation and detailing the inaccuracies in the review in a lot more depth - and a lot more specifically - than i've done here.
Now, whilst what I said in my email was accurate, and I had little motivation to lie or paint the company in a particularly positive light, Glassdoor really had no way of verifying that what I'd told them was true. Moreover I wasn't in a role related to hiring. Nevertheless, within a couple of days the extremely negative review had been taken down, and I was grateful to them for taking it down.
With that said, it sounds like what may have started out as a sane policy to handle complaints on a case by case basis has perhaps evolved into something rather less noble.