@Mushroom
I think a lot of it is that they only want to read stories that are exactly as they want them.
This isn't just a problem with 'asshole commentators' on SoL. This is a systemic and extremely longstanding problem. The 'asshole commentators' are just blunt and crude about it in such a way as to be easily dismissed.
I can't tell you how many movie reviews I've read that boil down to: 'Here's how the movie should have gone, and if it had gone this way it would've been a masterpiece, therefore this movie is garbage because it didn't go that way.'
The problem is that what the creator(s) created and what we can view is what they created. Is it fun? Is it perhaps also a masterpiece? Who can tell, when that's the review?
Usually, of course, they're far less blunt, and you have to read the whole review to realize that the pull quote 'The film-maker missed the mark significantly, rendering this just a bore. 2/5 stars' means 'The film-maker missed my incredibly brilliant idea and substituted their own vision, and I stopped paying attention once I realized they weren't going to do what I wanted.'
There are all sorts of bad commentators. In retrospect, I got most of them over and done with in the first 40 chapters or so, and most of the rest in a book or two. That's not much help to anyone writing shorter works, though.
My answer is always 'Sorry the story didn't go the way you wanted. I can't write it for everyone, and I'm telling it the way I intend to. By all means, go find a story you love. Life's too short to spend reading things you don't like.'
Or they're your answer:
I think a lot of it is that they only want to read stories that are exactly as they want them
As various pairs of my characters have been observed to say:
"Fuck 'em!"
"Or, better, don't!"