The issue is, it wasn't an exploit. The money gained wasn't like 5g average every attempt or something massive like that, and the money gained was directly reliant on the market of course. Sure it was a lot before the public knew about it, but of course if you found an overlooked or unknown method of making money , you would be able to make a lot.
In fact, I did something similar close to the early access, except I made game-breaking amounts of gold, but I wasn't banned. I'm pretty sure it fits the criteria for this "exploit" though.
1. Buy 3 40s~ exotic level 76+ armor
2. Buy 10 mystic forge stones, equating to roughly 10s~ each stone at the time
3. Throw 3 armor pieces + 1 forge stone in
4. Enjoy my new armor that has a 80% chance of giving me an armor piece that sells for 1.5g-8g
You bet your ass I sunk all my money into doing this whenever possible. The other 20% I didn't get a better piece of armor, I had a 50/50 chance of getting one that sold for only about 1g, or another 40s~ one.
And I know for a fact I could've done this even earlier, around 4~ days earlier for even more dosh money. I didn't see my method of "exploiting" pop up anywhere until around 1 week after I started doing it. I also could tell a few other people knew what I was doing and doing the same thing as well.
So, what's the difference between what I did, and what these people that just got banned did?