They can both see which side is going to win, how that side is going to win and that there isn't anything to do about it anymore. Why spend more energy?
So that's the first thing you could do when studying them: figure out why they resigned in a given position.
Have you got an example position?
Anyway, at your level, studying 2000-2100 games or so would work fine as well, and they make a few more visible mistakes and resign a little later.

I've been trying to study games played by GM, IM, etc. The problem is, they never finish the game. One or the other always resigns.
Why even study mate-in-x puzzles if the masters never even make it that far. It seems like the goal in chess is not to win by checkmate, but to force your opponent to resign.
My question is, why don't they finish the game? What am I missing?