I'd imagine that the reasons for patching trade exploits would be:

- The potential to do them unintentionally. Whereby people might do them by accident and not want to have this extra gold.

- Multiplayer interactions. It's a lot clearer to see when someone goes out of their way to pickpocket stuff. Less so when they're using some exploit to get more gold and resources. If not everyone agrees to using exploits/theft then it can cause some issues.

- It may simply be low hanging fruit. Something very easy to fix that someone does because they have a few minutes to spare.

- It provides them with experience. Knowing exactly how and why the exploit is possible, and the way to answer it means that you can prevent it from occuring in the future.

So while it's not the most pertinent thing to overall game balance, what with the ease of stealing and the fact the game throws literally tens of thousands of gold at you for doing nothing... There are still reasons to bother with fixing exploits.