I know you don't understand. Many players don't understand basic concepts. They seem to be under the impression that because this is a video game you should be able to do whatever silly crap you want, or that since it's a fantasy world there's no point in trying to be realistic with anything.
The truth is that, while a fantasy environment, they're still trying to create a plausible world, albeit one with magic and dragons. Even a fantasy world is still bound by rules for how things work, and they're generally trying to imitate our real world. So it is with carrying limits (can't carry 3.7 tons of stuff at once) and vendor stock/gold limits. In the real world a store only has X-amount of merchandise and Y-amount of funding on hand, and it works this way in The Elder Scrolls as well. Being a video game doesn't mean you have to throw all realistic concepts to the wind.
I agree with this. The economy is fine for the most part, however in my opinion there's a glaring option gap: Trade/Consignment. While I don't want merchants to have unlimited gold or huge gold amounts, it makes no sense to me that if a merchant has a 5000 septims robe I want to buy, and I have 5000 septims worth of merchandise that I could sell to him, but neither of us has enough gold to buy/sell from each other, there should be a "trade" option where you can have a temporary "sell" buffer of goods to sell to the merchant to reach the amount of credit needed to buy the item from the merchant. It would be done as a simultaneous sale to each other, no one could be left in the negative. Something like this would make vastly more sense then the unrealistic mechanic of having to visit every town and merchant in Skyrim doing nickel and dime sales to clear a single loot run from your bag. If a feature like that can't be added in an update, that would be a mod I'd be looking for, not a "10,000 septim merchant".