What you're describing sounds a lot more like Te than Ti.
Ti quits socializing because you're not interesting enough, not because it's impractical/inefficient.
Totally agree.
I don't shut people out because of "efficiency," I shut them out because either (1) I'm feeling anxious/intimidated or (2) they hold no interest for me.
Realistically, I think a lot of types operate from #1. I work in a building with close to 1000 people in it, probably, and so I pass a lot of people during the day. Some are generally cheerful and make eye contact and smile or say hi without provocation, others will avert their eyes and avoid allowing a connection. Sometimes I do one or the other, depending on how I'm feeling and whether it's someone I know.
In any case, assuming the rejection is personalized probably isn't accurate, I see it more as a blanket way for people to deal with social anxiety. When I get to know people better, it really does seem to be a personality style, not often as selective as this makes out. How efficient is it to have to evaluate each person and decide if they're worth talking to? People worried about efficiency tend to treat everyone the same; one rule, one style, no more thought about it.
For me I can't relate to small talk too much unless it's something I find really exciting.
I used to hate small talk. Part of the reason was that I was bored by it. Another reason was that I wasn't good at it.
The less I lived in my head and more I engaged the world, the better I got at small talk and the more interesting I found it. Nowadays I can enjoy chatting about lots of different things, as a way to get to know a person better, even if I usually prefer to discuss deeper more philosophical matters.
Energy Conservation:
Ti user not wanting to be bothered with speaking because they don't have the energy. That person most likely is a casual acquaintance to the Ti user and probably is someone who engages in small talk or idle conversation that takes effort on behalf of Ti user to engage on a consistent basis every time you see said person. This isn't personal. Just kind of a "leave me alone I don't feel like talking" hint but someone forcing conversation when Ti person is in this mode can lead to reason below:
There's that too. I'm good at social interaction nowadays, but I had to work at it... and it costs me. There's a steady energy drain, and when someone is sucking up too much of my energy or I hit bottom, I need to get out. The easiest way to protect my meager energy resources is to shut people out by reducing my replies to their comments and no longer making eye contact... in a way, pretending they don't really exist... because I don't want to invite them and encourage them to keep talking. But again, it's not typically personal, it's about my need to recharge.