Because they're all more examples of somebody not understanding how opinions work and you can only explain that people are allowed to disagree on things so many times before it gets really tiresome.
I can't tell you how many times I come to these forums (or go anywhere on the internet) and see this exact same series of threads and arguments: "I liked this game, therefore it is a good game." "I hated this game, therefore it is a bad game." "But I liked it." "But I hated it." "But it's good." "But it's bad." "Everyone who hates it is just a butthurt fanboy crying over spilt milk." "Everyone who likes it is just a blind sheep sucking the developer's teat."
I don't know what it is that makes the concept of subjective opinions, personal preferences or individual taste so difficult for certain people to grasp. That's why there's no need for "why all the hate?" threads, or, for that matter, any of the "I hated X therefore it sucks" threads either. All it is is immature people presenting their opinions as if they are objective facts to a community that actually does understand what an opinion is that then has nothing to do with this information, except to say, "One more member liked this game. Good for them?"
So yeah, basically it's just pointless and irritating.
