The Colorado shale deposits are largely on federal land I believe, (although some are under private land). That made it easy to shut that down.
I remember reading here (FR) a few years back that there was a project in Utah on private land that was also shut down by the feds. They just really don’t like shale oil.
The Green River beds in Colorado are Oil Shale: the oil is trapped in microscopic pores in the rock (Shale) which are not interconnected. It has to be heated to frack its own way out of the rock.
While it is accepted that the shales are the source of the oil in the Bakken, the actual production there comes from a low permeability reservoir between the shales, or from the Three Forks Formation below the Bakken, where oil generated by the Bakken has migrated. While it is Shale Oil, the wells are in a mixture of siltstone, sandstone, Dolomite and Limestone, and aside from being 'tight' and and having very widespread high oil content, are pretty much similar to conventional reservoirs in the same rock type.
What makes the resource "unconventional" is that the high oil saturation in the rocks persists over a large area, without much regard to geologic structures within the area. (There is some variation, but not as much as with more porous rock).
It is worth noting that on Federal Leases in Wyoming, Utah, and Colorado, a lot drilling was shut down.
If private land is not large enough to be the majority of the required well spacing unit, the nearby Federal mineral rights can, in some cases control whether or not the well gets drilled. Spacing units vary, and the Feds may have been able to shut down private efforts that way.