I never understood why people ask to trade a +3 item for another +3 item and a sum of gold. Thats just nonsense, 3 looms is 3 looms, only the base price differs and that difference is not 125k in this case.
I'll explain to you in the simplest of manners. Each item has a base price; correct. The difference of these base prices matter less at higher loom levels; incorrect.
Reason: Simply because each time you put an heirloom point into an item, it becomes permanent. The more heirloom points you put in an item, the more severe the ramifications become. Simply because the changes cannot be reverted.
Also, the rifts of tiers are of significance too. Mail Gauntlets are tier-2 gloves while Heavy Kuyak is tier-4/5.
Not to mention, there's a relatively high demand for Kuyaks at the moment. Maybe the demand is the biggest reason for the additional gold demand. Besides, anyone who knows a thing or two about bartering knows that you can always haggle the price. 125'000 gold is not carved in stone.