Fracked oil also declined because the easiest to frack shale oil was extracted first.  It's the low hanging fruit paradigm, the easiest to grab stuff is gotten first.  The best parts of Bakken were drilled first.

If the price of petroleum were to rise again that would reduce the economic losses of fracking, but the physics and geological limits are ultimately more important.

The decline of fracking in shale gas fields in central Texas and Louisiana / Arkansas were more due to depletion than the lack of profit.

I recommend the reports of geologists Art Berman and David Hughes for documenting the geology of fracked oil and gas.