Interacting with accounts in a huge, pseudo-anonymous social media sites based on discussion with voting systems is quite different from interacting with people in real life. For big sites like HN and most subreddits, the users may as well be anonymous. HN goes a step further and deemphasizes usernames a bit by making them lighter in color and smaller compared to the black body text. How do you build a "close in group" on a site this big with not a lot of emphasis on who you are? I've been on smaller message boards where you can actually get to know people and have an avatar and some public info about yourself attached to every post. It's a different experience in that case, for sure.
You wanna talk about how humans work - strangers in real life also don't just walk up to you and start talking about Reddit account security out of the blue! We also don't trust a talking head on TV or on the radio just because they're human. Relationships are built over time & higher trust has to be earned. Even if you're referring to the fact that most of us probably live in a relatively high trust society, that doesn't mean we trust our neighbors' opinions on strong passwords (or whatever) just because we trust them as our neighbor!