Very simple: the law of supply and demand.

The problem you are running into here is the fact that just about everyone rushed to cap their 1st 50 DoW/M class, and hardly even touched their DoH/L classes. So naturally you will have way more suppliers of the said item, then the crafters that can make use of the said item.

Solution: Level up your crafting so you can make those items for free, and not have to pay 90K to purchase it.

jc