Airlines missing the obvious way to save weight on planes?

It seems that airlines are taking heroic measures to save weight on their planes - from lighter seats, less water in bathrooms to sharing manuals between pilots. The NYTimes articles quotes one airline as saying every 25 lbs saved on their planes saves $440,000 per year in fuel costs - which I assume is across their entire fleet, not per plane.

But it seems to me that they are missing, or at least keeping quiet about the most obvious way to reduce the weight of their planes - reduce the passenger load they are carrying. Baggage surcharges are unpopular and unless uniform a point of competition between airlines, however attempts to charge over sized passengers for two seats are controversial - just how do you define over sized without forcing a passenger onto scales, something about as unpopular as trying to back scatter x-ray them for security. So maybe passenger load could apply to just bags - we all know the people who carry the max just because they can - and usually have bags full of stuff they just don't need, even for a short trip. Carry on bags are often a source of abuse because they seldom get weighed (I've never seen a weight check on them, just size) and people always manage to loadup with extra laptop bags, baby bags or handbags stuffed the brim with junk.

How about the full price assumes you take maximum baggage weight, say 50lbs, but if your combined carry-on (everything but you) plus checked baggage weighs less than that weight then you get a discount - and as always an overage in the baggage department still attracts a surcharge. This will at least incentivize customers to reduce their baggage weight and pass on fuel savings to them.

Another way would be for planes to have a greater variety of seat sizes and spacings with appropriate pricing - but not such a difference as between coach and business which get an additional level of service too. Passengers would then naturally pick the appropriate seat that they are comfortable with and pay a small premium accordingly. Some airlines already have premium seats with extra legroom, but extra width and legroom might be even more attractive - if you can figure out how to arrange seats to accommodate that (maybe a diagonal isle?).

Yes, all crazy ideas I know, but it seems like airlines are looking for crazy ideas!