Because HackerNews is not some haven of rationalism, especially if the not-west is involved. A well cited well reasoned opinion will be downvoted to oblivion and accused of astroturfing if it goes against majority opinion in those cases. I've seen far too many threads about some non HN saturated country where the only commenter that's actually from that country gets downvoted to oblivion for trying to bring in a modicum of nuance. Even when they're like GP and preface their comments with "I agree with the orthodox opinion but...".

Maybe GP doesn't want to get stalked by some paranoid HNer who thinks they're a Russian spy. Maybe they don't want to lose some karma dependent feature of HN on their main account. Maybe he was a lurker and this specific topic was what was important enough to finally make an account for.