Mat importers gold farming

Why is Blizz allowing this to go on. I’ve been told by a GM that it is against the code of conduct yet there are 1,000s of mats brought in on a very regular basis and undermining our AH traders and local farmers and crafters. If you buy multiple stacks to resell the following day they bring in more and sell for cheaper than the price paid the day before. These are low lvl toons used as mules and the gold doesn’t stay on the server. Apps like undermine should be banned and toons carrying mats they are unable to farm when transferring servers should be blocked from transferring just like the cap on gold for low lvl characters.