I was helping a customer who discovered their product reviews app was grouping reviews on the collections (against Google's policy), and he got me thinking...
...which is never a good thing on a Monday...
For years Google's been fighting websites that abuse review structured data.
Google wants to help customers find the better pages but every year they have to tighten or clarify their policies because some websites abuse them or find loopholes.
I remember a ton of websites getting hit in 2017 for combining reviews.
Then the whole business / store reviews that people were using in 2018 to get Rich Results on any page, that gets kicked out by a new policy in 2019.
The thing is, most of these policies already forbid these loopholes already. Don't group reviews onto unrelated things, put the review on the page it was reviewing, etc, etc.
Google doesn't call-out everything you shouldn't do, they list what you should do and expect people to avoid the really dark gray areas.
Crystal ball time...
Given this year-over-year abuse and policy tightening, I wouldn't be surprised if reviews are removed from the Rich Results in the next few years.
We've already seen that with those author / profile photos where Google used to show the author's faces in the search results.
All Google has to say is that review data will now become purely algorithm driven and then every review app has to dump most of their SEO features they sell people on.
(One benefit will be JSON-LD for SEO's code will become much clearer... supporting over two dozen review integrations is taxing at times, especially when a review app has poor support)
There already are a lot of search enhancements that are already purely algorithm driven: Sitelinks, featured snippet, people also ask, related searches, etc.
Making reviews Rich Results into one wouldn't be a stretch.
And given some of the crap Google is fed about reviews, I don't blame them either.
Until then, I'm just going to keep following Google's guidelines and do my best to call out violations to customers when I see them.
If you'd like a structured data app that follows Google's guidelines and is more effective than the rest of the industry at winning Rich Results, you'll want JSON-LD for SEO.