As someone who neither likes nor dislikes G'raha, I'd have to say the main reason people dislike him is because they don't (or can't) appreciate his boyish charm. He's kind, earnest, and helpful, and... not everyone likes that in a character.

Plus he's been getting a lot of screentime as of late in order to establish him as a core member of the cast after spending all of Shadowbringers' MSQ as the deuteragonist, and having a character you don't like on screen is going to grate on peoples' nerves.