Due to the cyclical nature of posts and the exhausted moderators trying to mod all of them, it's quite effective for "organic" growth. Many companies use these methods to grow, because it's way cheaper than paying for ads and users online are simply too gullible to catch on. And even if they did, you can just delete the thread and make a new one later on.
It's the same strategy used in TikTok where the influencer subtly hints at the product rather than overtly talking about it (perhaps as one slide in a slideshow), and then when a commenter asks what they used, the influencer replies with the name of the product.
For example [0], there have been large scale astroturfing campaigns for things like games, posting large numbers of comments to influence users.
[0] https://old.reddit.com/r/Games/comments/1ot0nvg/game_dev_adm...