To be frank, we were headed in that direction anyway, ubiquity of cheap and accessible high-quality writing generators just accelerated the inevitable.
For a very long time astroturfing was only viable over broadcast channels and [therefore] was expensive enough that only the really large corporations could afford to engage in the practice. With the advent of internet forums that could be arranged by any larger marketing agency and became available to any larger entity. With the advent of so called "user generated content" astroturfing really became easily accessible to any medium sized entity.
It has always been a race to the bottom. Reddit and Youtube are well known examples. If you follow any niche there whatsoever, you can easily (especially retroactively, because there's usually a ramp-up period) pinpoint a time where some astroturfing entity either launched a bot army or bought out mods/creators.
LLMs have dropped the cost of astroturfing to such a degree that not only it is now viable for any individual dropshipper to engage in the activity, locations with conversions previously too low to matter became viable attack targets. Everyone with several dozen euros and some hours to spare can now absolutely flood every corner of the internet without extremely strict authentication.
Some places are more resistant to astroturfing than others, though. I would suspect that if some few days old accounts started praising Foobarized in every possible thread here on HN the admins would ban this keyword quite quickly. One needs to be slow and careful. It requires pre-creating a bunch of accounts and leveling them up with some casual comments here and there so that when the actual astroturfing campaign starts (buyer not yet determined), the accounts are primed and are accepted as part of the community.
The internet is dead and has been for some time, it's just that we are too afraid to admit it to ourselves while actively seeking closed gardens of confirmed human-to-human communication.