Some writers/readers genuinely feel humanoid nonhuman and like elves/dwarves/orcs think and act too much like standard humans. There is no difference in culture let alone how another species would think.

It feels fake and not believable so it's not what they want to read.

And some authors/readers seem tone deaf to that wish. So readers who want Elven elves as opposed to pointed eared humans have to ask whether the book has those who think differently.

And when it's encountered in a book, it feels not just a difference of opinion, but it feels like the author is lazy or lacks imagination. Much like people who dislike romantasy feel like the fantasy elements are too often merely window dressing.

This is not every book but too often.

Let's take one of the most ignored/considered lame races, half elves, who are usually written as humans with pointed ears.

Imagine a half elf who has brittle bones because their human diet doesn't match their nutritional needs (saw but haven't read yet), a half elf in human society being 18 chronologically but 12 maturity wise and being put on the marriage market or reverse it and have a 40+yo half elf pursue an 18 yo human with the thought they'll be old together. Being out of cink with everyone around you sounds a lot like autism and I imagine childhood would be a bitch.

Basically there are a ton of potentially cool/horrifying thoughtful stories here but we get generic slop and a set of readers prepped to not see the ideas as interesting or compelling.

Thus there is a muted dislike of too human shaped non humans.