When I ordered my TBs (elsewhere) they only had three in stock. When I asked how many more they were getting they said that was it. TBs were not made in large numbers because the only reason they existed over the 780ti was the extra vram. Nvidia knew this too.
3gb vram will not be enough for 4k into the future. That's why TBs are £600 now and not the price of the 780ti. You're paying all of that extra for Nvidia to give you the vram you need, not the rationed amount they want you to have (to keep you coming back).
People say vram is a waste of time, yet, I know people who got laughed at for paying stupid money for 2gb 5870 Vapor X. Thing is, those cards still cut it in CFX at 1080p, the 1gb ones ran out of vram ages ago.
So YPYMYMYC really. I had no issues with dropping £695 a card on mine because I know power wise they have enough to sink a ship and vram will last. I could have spent £150 or so less on 780tis only to find in a years time they need replacing.