Cruise missiles fly (self powered) at very low altitude from great distance and the pop up at the end of the flight to come down on the target from
the top. Many things can go wrong along that flight path.
JDAM is dropped from a plane at high altitude and just glides down a rather linear path. In addition to the GPS it can use inertial guidance in case
of jamming. I'm not sure if the new tomahawks use that or not since it's mostly classified.
Anyway, make a long story short the easiest way to get from point A to point B is a straight line not weaving between hills and valleys.
Hope that makes sense