yeah it's funky. I think that since they don't limit your bags by space, they try to offset it with weight. So things that would naturally be bigger and things you wouldn't normally be able to carry in a bag simply are heavier in the game.
That's my theory. Still doesn't explain why a water keg or a crate that can literally fit 2 people inside weigh less then a painting, but it's as close as I can logically get in my head.
