Why gems are much better loot than gold

It's one of those moments when I think pointless things about the implications that games have (but we all ignore).

I'm going to make some gross generalisations here. If we say that an average gold piece is about the same size as a modern coin, that means a piece weighs 15g. A hundred coins weighs a kilo and a half. A thousand gold pieces weighs 15 kilos. Try putting that into your backpack. A large chest (1x0,25x0,25) full of scattered coins would contain about 150.000 coins. A sizeable fortune you can retire on. That also weighs about 2 tonnes and a quart.

The same values (1gp, 100gp, 100gp, 150000gp) expressed in gems and jewels:
1gp: a flawed semi-precious stone
100gp: a nice piece of jade, amber or amethyst
1000gp: an emerald or sapphire or two black pearls or ten pieces of jade
150000gp: 30 diamonds or exceptional emeralds or rubies
(figures roughly taken out of Pathfinder, I'm sure the editions differ on this)

What would you rather haul out of a dungeon, a chest weighing as much as a big car or a fistful of jewels?
One thing I like (in theory) about old-school dungeon raids and the gp=xp rule is that this treasure salvaging can become part of the strategic and logistical challenge. Part of the decision-making process as well as part of dungeon design. I rarely if ever see it being taken into consideration. The fact that encumbrance rules mostly suck is probably no small part of this.

Back to sensible things.