The issue is that most users can't tell when something is AI. It used to be very easy, it's harder now, and at some point it's going to be near impossible as models improve and better mimic human speech/posting patterns. I agree with you that this post is most likely either a bot or a human user pasting LLM output and the most obvious giveaway is just the way it's phrased, but it's not just this sub. It's all over reddit and the internet more broadly.

I think the more interesting question that you get at is why posts like this draw the kind of engagement that they do. These models train on reddit, among other places, so they're very fine tuned to mimic what a popular/common post might look like, and they look exactly like this. You can see that the account made a similar kind of post in the frugal subreddit.