And you agree about the social contract. Actually, it even exists online, even with the resign button. If I resign 50% of the time on turn 6 when we play, no explanation given, you would pretty soon want to blacklist me. So even online, even though some of us don't expect an explanation, we do expect that there is a legitimate reason.
This whole thread is absurd. If I screw up the opening in chess and put myself in a losing position against a competent opponent, I'm not going to sit around for 30 minutes waiting for my inevitable loss. I'm going to resign and move on to the next game. I can see how you might derive some enjoyment from gradually exploiting your advantage over many turns picking off my pieces one-by-one, but what incentive do I have to participate in that? I'm not a masochist.
Similarly, in Dominion while I can see how you might enjoy playing out your engine over several turns after you gain an insurmountable lead, what incentive do I have to participate? Why should I suffer for 10 more minutes while you parade to victory? Accept your victory and move on. Resigning is never unsportsmanlike.