The problemi is that the majority of questions here are anonymous, and most of those questions aren't the least delicate or personal. Some are about sports, or general questions that apply to nearly everyone.
If I answer a question that is personal I don't want to share who I am but if it's not personal and just a point of view I'll answer as my screen name. Not hiding anything, more like deciding I don't want my screen name associated with anything that someone can track me with because they agree or disagree with what I write.
That being said I've only posted one anonymous reply and I can't even remember what it was. Ha!
It's a very good question!!. Yes, I also wonder the same thing about such users who do that. One good reason could be trolling, that is to troll, as you know trollers are there everywhere and being anonymous makes it easier for trollers to keep doing what they do.
Of course all anonymous users are not trollers, not at all. I am not saying that. Please note.