Or, you know, you've just read the old books already because they came out 10 years ago and that's a lot of time to read.
I doubt it has anything to do with "romantasy" as a genre, anything that has people actually reading books, on a regular basis (as opposed to the people who mean reading as consuming one "notable" novel a year).
In any case, epublishing has made a lot more books available and filtering through them was a difficult task even before AI increased the output dramatically.
I've been saying for a while now there's a large untapped market for actually effective recommendation systems (almost certainly human driven given the demonstrated limitations of computer systems so far), as mentioned it was a problem to find "the good stuff" even among just self-published pre-ai books, now it's way beyond that.
I guess to some degree it's the same basic problem as spam filtering, but considerably more nuanced and difficult.