i think the actual reason "homestuck is bad" is such a prominent opinion is genuinely just because of the divisive ending (and partially the post canon stuff i guess). homestuck is a big investment, in terms of time and energy, even if you didn't read it as it was releasing, so when something that you've put so much effort in and genuinely liked (because, well, if they didn't, they would've dropped it. homestuck is not something you can just casually consume if you don't find enjoyment in at least some part of it) ends in a way you find disappointing, that colors your whole perception of the thing.

it's easier to pretend that homestuck was just bad the entire time and all the good parts you liked were "accidental" or good in spite of the rest of the comic, instead of just admitting that something you were invested in took a direction you didn't like or actually just trying to re-read the comic without your own preconceptions of "what should've actually happened" to understand why the story actually took the turns it did