Elvia cups max prices if out of proportion and 2bil maximum price is the main reason not 1 is even willing to consider selling them.
I have Pre-Order for over 2 months and nothing:

Let's take Cup of Earth's Sorrows as example:

Magical Shard x30 = easy to obtain trought MP.
Shard of the Furious Night x50 = https://garmoth.com/grind-tracker/global/18 = 6/hour
Shard of the Tearful Night x50 = https://garmoth.com/grind-tracker/global/14 = 10/hour
Shard of the Drained Night x100 = https://garmoth.com/grind-tracker/global/15 = 6/hour
Black Stone (Weapon) x100 = easy to obtain trought MP.

We're talking here about 3 different spots and these will bring you festest farm with a total of 22 hours of grinding.

Is 22 hour of grinding worth 2bil? maybe back in 2015 (250-300m/hour was the highest farm), but for now definitely no!

Kindley fix the market and remove staff controled limitations from everything, Supply - Demand will control it

The issue is not that it takes 22 hrs to grind it. The issue is that 2/3 spots (water / lighting type) are less money/hrs than centaurs is. If other serendia elvia spots gave similar money to orcs, then people would grind these spots too. As it stands now, some people have thousands of the fire shards, and some still have a good bunch of the thunder ones from back when bloody was broken (or they play a class that still makes bloody look broken). But the water spots have never been popular because of the low money/hr compared to other spots that can be grinded with the required gear. Buffing water spots (maybe make imps finally worth it, and add a 2 person spot that's fun and worthwhile) would help bring a lot more supply to the market. 

Of course, increasing price to make the lack of money from water spots worth it is also an option, but I'd rather see other spots get some Love, especially group ones, to solve the supply issue that way. 

why would you not just grind it out yourself? I even grinded out my 2 vell upgrades myself.

Those spots are low income, ofc no1 wants to grind there and IF its for their own cup.