For some numbers, a 777-200 carries 313 passengers, weighs 135k kg, carries up to 100k kg of fuel, and has a max takeoff weight of about 250k kg. 313 passengers and luggage, averaging 100kg, weigh just 31.3k kg. Your ticket therefore pays for your weight, plus 5x your weight in airplane structure, plus (up to) 3x your weight in fuel.
If you don't show up, they're still carrying 8x your weight anyways, so saving 200kg isn't that important.
(PS: apologies for the 'thousands of kg' units. I thought it was more readable than Mg or fully written out numbers.)
Just write tonnes (= metric tons)?
What about if you are flying long haul and linking up to a domestic flight on another airline? "Oh, we can't help you because your previous flight was delayed due to weather/mechanical/congestion.you should have flown on one carrier even if the price was 2x"?
Airport congestion is a big issue in the US, as is weather related delays.