Haven't watched, but victory in games like this is psychological. If you kill a player, take a few factories, or control a lot of map area with artillery, you'll win the game. It's actually quite psychologically draining to go up against some of the more artillery-heavy factories, because you always feel like you don't have good options.

I wonder whether resigning might be more commonly correlated with having opponents heavy in such units (like firewalkers, tremors, or lances, since those are the most psychologically terrifying units, in my experience).

yes everyone tells you it´s purely psychological when you die to arty spam.
at the same tiem, NOONE in my 6000 games could ever come up with a good solution to the problem. If i ask what i should do, i will get: "I don´t know, but don´t resign".