Oh, they did try breaching them with c4. It failed miserably, as the bocage hedgerows weren't just tall bushes. They were massively overgrown earthen walls mixed with stone walls mixed with incredibly tangled roots, all combining to form something nearly impassable. Accounts of trying to blow them open exist, and it didn't work. The only thing that did work to an extent were the hedgerow cutters, as those could slice through the root structure and thus clear a gap. However even those were of limited success, as only around 100 tanks were ever fitted, and, as the first through the gap, they were often knocked out first too.