you make it sound so easy, but in 216 B.C. it had never been done before. you discount the likelihood that the center could break, which was why sun tzu in the Art of War advises that the double envelopment maneuver should not be used. hannibal executed the maneuver perfectly, while other, lesser generals could easily have botched the maneuver, by waiting too long to order the cavalry on the flanks to close or simply because the center falls apart. military generals throughout history have sought to emulate hannibal's double-envelopment at cannae, and few have been able to do so. the germans certainly could not do so in world war I, although they came very close, as the Schlieffen Plan was based on the battle of Cannae, a battle two thousand years before WWI. And the Romans did want to meet in open battle at Cannae, at least Consiul Varro did. The previous Roman dictator, Fabius, was the one who wanted to avoid open battle, but the Senate would not renew his term.