Too expensive. There are two techniques, Freeze Wall and Toe to Heel. Do a google search with the keywords Green River Freeze Wall.
Eventually, after Bakken, Eagle Ford, etc go dry and price goes up, then the Green River will be economically reasonable and technically feasible.
This is no different from the Bakken, Eagle Ford, or the Alberta Tar Sands. 10-12 years ago there was very little profit to be made producing there. But, under Bush, the price of oil quadrupled and there is very good profit to be made in those places
What policies did Bush implement (that Obama has obviously carried on) to make the global price of oil explode like that?
True for the first two, but in 1963 Sun Oil invests almost a quarter-billion dollars in the Great Canadian Oil Sands project. That facility remains in commercial operations today. Other commercial operations started and stopped going back to at least the 1920's.