On HN, I tend to limit my responses because I usually end up being attacked for something I have nothing to do with, by virtue of some grudge the commenter has with Google. If you want to call me out for my own work, go ahead, I value feedback greatly in areas that I can control. If you have useful commentary, I'll try my hardest to make sure that people with understanding in that area see your comments. But if you just want to yell at me by virtue of who pays my salary, I find that all very unenjoyable and would prefer to not be involved.
I also notice that lurkers with blogs tend to like to take quotes from HN and convey them as the official word of Google out of context, which I also don't like being involved in. Learned that lesson my first week at Google :)
Finally, one also ends up attracting the crazies that email me threats against other Google employees. All those get forwarded directly to Security Operations and don't get a reply from me.
HN is a pretty big community these days and isn't quite the bastion of sanity that it once was. This limits how open many people will be with the community more than any policy.
Sound alike the whole reason is to make their device owners able to make better choices.