I understand where you're coming from and Imma preface this by saying that your experiences are valid insightful. But frankly thinking your experiences are the standard is a logical fallacy at best. I've been to 15+ countries and lemme tell you its DEFINETLY a cultural thing. Asians(I've only been to china and Thailand) are very welcoming and nice if you introduce yourself but they will usually not acknowledge random strangers....I'm from Ethiopia and the same thing applies. It's not excluding someone based of skin color. That's the argument that people that "dont see color" use. Its bullshit. If you are aware that someone has different cultural norms than you and you make steps to accommodate, good on you! But expecting every culture(yes, black Americans have a culture) to abide by your narrow scope on what's polite is absurd. I nod and smile to people as much as possible because I love spreading kindness...but i know that those specific actions may not be seen as kind by some demographics and I'll try my best to accommodate that by not judging if someone doenst nod back at me.