Lots of oilmen got burned in the last boom-bust cycle and are inclined to wait a bit. But certainly the oil rig companies are doing well! So at least some oilmen are investing.
Also there is the little matter of reasonable places to drill, in expectation of hitting oil. The last big find was many years ago - it may be that the expectation of exploitable new areas has reduced the investment activity. Peak oil effect.
Peak oil - at least as couched by devotees of "dieoff.com" and "the great supercycle" - is right up there with "Earth Changes" and little green men. CTCAM standard material. As for your comment about tapping into the untapped - there are plenty of fields IDd that have not been tapped, right in in CONUS. I'm literally sitting on top of one. [My degree - Geophysics, 1984].