which I assume delegate because they like what we're doing with our curation

Let's be real.. Most of them really delegate to get attention or just think that if they delegate, OCD will start voting them xD (Not talking about major investors/supporters)

Not saying OCD does it, but I heard it from multiple people that they have delegated for that sole reason. I also ran my delegations rewards distribution bot on a community I admin, so I got some sort of a first hand experience regarding why folks with smaller stakes delegate usually, considering I had to interact directly with most of them, and that seems why the majority of them do it, whether they say it or not.
They get unhappy when they don't get special treatment, or WORSE, they are surprised when their plagiarism or AI doesn't get ignored.

But I do agree that there are also many good supporters, who do delegate because they just like the community and what it's doing.

Back to the topic, however. There are Multiple projects / communities who are doing some sort of vote selling one way or another. I don't want to directly name some, because I'm sure I'll forget others.
But some Brothers for example justify their hold x and get vote selling scheme with "we have a minimum standard of 500 words for posts" (To be fair, that one doesn't offer it as the only reason to hold their token, but still.)
Another justify their points usage as the initiation of the voting on the post is "manual". Or a Neo-vote seller justifies it with "it's only a couple of bucks max" and hiding the rest with other forms of "lotteries" as far as I know.
Then we have the whole circle-jerking aspect, with groups of probably actual friends only voting eachother.

The line really gets blurry sometimes, and I'm not sure if such practices would eventually get abolished as the userbase grows, or it would actually get worse.

We certainly hope for the former!

Because I do think with more options and varieties, it gets easier and less time consuming to find curation worthy posts from authentic authors, and there would certainly be better distribution among them.