Can you link some you've recently encountered?
To pick an example from a different domain, when one commenter accuses another of being a communist shill for China (a ridiculously common recreation), it's easy enough to look at the latter's history. Frequently you'll find that that user has been posting about, say, Julia programming, and house prices in Boise, since 2014. (I made that up but this is typical.) Could they still be a communist agent? Sure they could, but this kind of thinking quickly becomes madness.
Occam offers a perfectly good null hypothesis: people just disagree. HN is a large enough population sample that you're going to see users from every background and disagreement about every topic, including on every big tech company, which many users have strong feelings for/against. For some reason, though, internet users aren't satisfied by that and crave much more sinister explanations when things they dislike show up in the forum.
There are cognitive biases underlying this (I've written about them at [1] and [2], if you or anyone is curious), and I'm not seeing any information in your comments here that isn't easily within the normal range of such biases. Real astroturfing and other abuses exist—you can look through the endless history of [3] to find plenty of times where I talk about that and a few cases where we actually find it. But there's no question that real abuse is dwarfed by the imaginary abuses that internet users love to speculate about. Therefore the rule is: if you're to going to bring this up you need something objective to go on. It can't just be based on memory and feeling, because memory and feeling are entirely unreliable on this.
[1] https://hn.algolia.com/?dateRange=all&page=0&prefix=true&que...
[2] https://news.ycombinator.com/item?id=23308098, https://news.ycombinator.com/item?id=23716395
[3] https://hn.algolia.com/?sort=byDate&dateRange=all&type=comme...
But please don't dismiss this so quickly. I have seen pretty harmless types of post getting brigaded or flagged pretty consistently. This happens more often to new or less known users - who might have something interesting to say but are quickly shut down.
Now, we can always blame it on different tastes or whatever, but knowing that certain companies engage heavily in "online presence" wouldn't it be naive to think they don't operate on HN too??