Oh ho ho. Guess you've never hung around the Alaska terminal at LAX around 500p-800p on any weeknight. They schedule LAX-SEA flights to leave about every 30-45 minutes or so, but invariably at least one is cancelled and the loads combined. It's absolutely standard practice. I went through a six-month period in 2000 or '01 when I almost never came home on the flight number I was booked on.

I don't know if it's because they cancel southbound trips for the same reason and therefore don't have the metal at LAX for all their published northbound runs, or they knowingly publish more flights than they can operate and just cancel the lightest-booked one, or if it's cheaper for them to overnight a/c on Mexico services at LAX than to fly them up to SEA and back one-third full.

But if an airline person tells you soberly that trips are "never" cancelled because of light loads, don't believe it.