Every review I left for Amazon products (Amazon EU) got rejected until it was diluted into nothing. The explanation was always vague, listing a dozen possible reasons, none of which fit what I wrote.

On non-Amazon products it's a coin toss for negative reviews. Many are published, some are not. Can't explain why.

Google is not better, negative reviews I leave on Maps are published very selectively. Maybe big-tech found a way to monetize this too. I know sites like Yelp are more or less an extortion business where you pay to get negative reviews wiped.