They dropped a GBU-43/B which is a concussive bomb. Not to be confused with the GBU-57A/B Massive Ordnance Penetrator (MOP).
Another reason to drop the GBU-43/B is a pissing contest to see if the Russians will drop their Father of All Bombs or FOAB - Aviation Thermobaric Bomb of Increased Power (ATBIP) - (a thermobaric bomb) weighing in at 44 tons of TNT.
Popcorn anyone?
The penetrator bomb would be less effective for random shallow tunnels and caves than against a known location, deeply sheltered single critical military (political) bomb shelter or weapons facility.
Thus the Iranian a-bomb facilities are a penetrator target, as are the NORK bomb shelters and weapons test tunnels. The Muslim targets in the hills are the better air-aerosol explosive that kills over a larger area.