A bunker is a grave by another name. Fortifications were meant to channel an attack not as an end in itself, if the rag heads cannot maneuver off of the fortifications in strength, then all the Israelis have to do is isolate and eliminate.
Bunkers were the Japanese tactic in the Pacific on Iwo and Oki and other places. They were expensive to clean up but they did not survive. We did not have the bunker busting weapons and precision capabilities that we (and Israel) have now.