No I guess it had not yet occurred to me that socially active people should avoid community seating so that socially averse passengers could eat together in quiet seclusion. It takes a lot of effort to twist my mind into a view as confusing and convoluted as that.
Then yours must not be the twisted, confusing, and convoluted mind that came up with the idea of a Quiet Car. Clearly, many passengers don't want to socialize with other passengers. Many trains (though not LD ones that I'm aware of) have Quiet Cars for precisely this reason.
Virtually every other restaurant in the entire country works exactly the way you want. Is that really not good enough?
If, in "virtually every restaurant in the entire country", "everybody keeps their distance and nobody expects to hear so much as a peep from anyone they didn't explicitly choose to eat with", is it that outrageous to want the same on Amtrak? When given the chance, even the most extreme extroverts choose NOT to eat with strangers. Why not give everybody that chance?
I'm introverted myself, but that doesn't mean we have the need or the right to go around forcing our social aversion on others. When I choose to eat in the diner I expect to join the conversation. If I don't want to participate I either take my food to go or I have it delivered or I eat in the snack car, or I just don't bother eating that meal. There are more than enough options to work with.
Wait. I'm sitting quietly, enjoying my meal and not bothering anyone around me, but the person across from me feels awkward and keeps trying to drag me into a conversation in order because HE wants to, and yet I AM the one forcing my aversion on others?
Let me make it clear that the situations and opinions I'm expressing are not what I actually DO onboard. These are my PREFERENCES. What I actually DO is travel with my wife. We've taken a train journey most summers for the past couple of years. Approximately 90% of the time, the two of us are seated with two independently-traveling strangers. To the best of my knowledge, we've only been seated with couples/pairs on TWO occasions. Once, we were seated with two co-workers. The other time, we were seated with another young couple. All of the other times, we were seated with two "singletons", although we've had several breakfasts and one dinner by ourselves (a late seating).
So, for most meals, we're the only people at the table who know each other. Neither of us are extroverts, but we try our best to talk to the other people at the table - starting with the usual icebreakers like where you're from, where you're going, etc. Most of the time, that's about it for talking. Maybe somebody comments on the weather, the scenery, the food, etc. once every few minutes. I'm fine with that. We pass the meal in what I'd call "companionable silence". When I use figures like 40% of the country being introverts, these are the sort of people I think of - people who will talk if they feel they have something to say, but are happy to sit quietly when they don't. I've enjoyed those meals.
Sometimes, we get people who won't talk at all - one word answers to our questions, & clearly no willingness to talk to us. Since my wife and I obviously know each other, there are times when I want to say something (the food, the scenery, etc.), and I try to direct my observations to the whole table. If they don't respond at all, my wife and I just talk to each other. As I said, we do our best to try to include them at first, but if they won't talk we just talk to each other.
We've been seated with someone I'd call an extrovert - someone who talked through the whole meal - maybe two or three times. Always a guy travelling by himself. That's fine too. I'll happily chime in whenever I feel I have something to say, even if the guy is carrying the conversation. Chances are the other single diner isn't saying anything.
What I'm saying is that I'm fine with ANY of these situations. I don't get angry with the guy who talks during the whole meal - after all, it's community dining. I don't get upset with the people who don't talk at all - I don't feel that it's their responsibility to keep me entertained. I'm perfectly happy with any level of conversation.
I just don't understand why you (and others) can't just live with the tablemates you have.