It takes ... a surprisingly small number of reviews on a just-released (or not yet released) film to either tank it or send it to the top of "highest rated" and "trending" lists on IMDB. I regularly see 10/10 and 9/10 reviews from obvious bot networks on fairly obscure indie films that aren't even released yet. They have similar trademarks, e.g. large number / large number found this helpful. Presumably the bot network operators know or suspect that IMDB factors certain reviews in more heavily when determining which films are trending or it helps evade some algorithm designed to detect trolls.
Why the 4/10 reviews? Maybe this an attempt to tank films from rival companies. Again, if you're looking at films with a small number of ratings and 9+ averages, that's rarified air. IMDB regularly recommends new movies like this to me, because I watch a lot of movies that just come out. So if you can bump your film nobody has heard of with dozens / hundreds of reviews and get a few thousand sales out of it, while knocking a competitor film down a couple rungs, that's probably a good deal.
My guess is most of these networks are actually paying individual people to leave reviews, requiring that they contain some list of buzzwords. Your examples seem definitely like bad AI, but most of the ones I've seen are just written by people with very poor English.