It's not manufactured that is for one. People are simply not as dumb as blizzard thought they would be.
Second, being casual have nothing to do with gold you have. Someone proficient at AH flipping could earn it in couple of months with near zero played time.
Third, even casuals could have multiple alts in WoD/Legion and amass milions of gold.
Fourth, people blame blizzard for:
1. Not announcing it will be limited at the start of expansion.
2. NOT ANNOUNCING IT AT ALL - that's absurd we had to catch them red-handed.
3. Removing it for zero reason, since there was no real reason - it's pretty obvious it was cash-grab.