Confident People Wave

So I don't get it, when there is no one around and you walk by someone what do you do?... You wave or say a quick hi. I've always been a waver so I really don't understand why ppl see someone they know our know of, and they don't say hi back and just don't know what to do when someone does say hi.

My answer its that confident ppl say hello. At work and church theres a long hallway that I'll occasionally walk down and someone usually passes me. Its not just me I swear bc ppl will be in front of me and give a hello to a person coming down and they'll put their head down like they didn't hear it or something. Whether I know the person or not I'll always give a quick hi bc you never know what's going on or how it can brighten their day. I'm just generalizing but the ppl who say hi to me when they pass are usually more confident than those who do not do anything and might be afraid of rejection and not getting a response back if they do say hello.

Eh anyways, just something I've observed the last few weeks. No matter what for me though I'll still wave.