NVidia has been sold out at $699 for a very long time. You cannot purchase a 1080TI from NVidia through that link and haven't been able to for awhile. You missed the most important part of that entire link "Out of Stock". That's why you see them selling for nearly double that if they're still in the box with a warranty.
Agreed, I should have included that. If they are brand new, people sell them for insane prices. But once used, the prices become a lot more reasonable.