As with any complex operation, the factors for the slow breakout of the allied forces from normandy are myriad, but it can be distilled into a few short points.

Firstly, consider that every can of food, every bullet fired, and every GI, had to be shipped across the English channel. The supply situation in normandy was tenuous from the start, and two weeks after the landings on June 6th the channel was hit by a truly brutal storm that badly damaged the mulberry artificial harbors, and slowed the buildup of allied forces.

In the British and Canadian sectors, the stalemate was the most pronounced. This area of the front was under the command of the British General Bernard Montgomery, whose legacy is VERY complicated and controversial so I won't go it to it here, but suffice to say that one of the criticisms most often leveled against him is how over-cautious he was. The planning for overlord had Monty taking the city of Caen on d-day, but he failed to do so, and the northern half of Caen wasn't captured until July 8th, with the rest being captured two weeks later. This stalemate on the eastern side of the allied front held up the advance considerably.

It is worth noting however, that Montgomery thought that his stalemate was useful, as it tied down elite German panzer units such has the Panzer Lehr division, and prevented them from opposing the American breakout under Bradley in the west.

That leads into another factor of the slow advance; the allies were facing incredibly tough German resistance. While many of the soldiers garrisoning normandy on d-day were ostruppen, or understrength divisions, in the weeks following the landings the elite Panzer Lehr, and Hiter Jugend, divisons were arrayed against the allies. These divisons were populated by fanatical nazis, and equipped with the best gear, including tiger tanks.

To loop back to your original question; the bocage absolutely played a factor. The terrain has been described in German letters home as "a defenders dream". Not only did it provide perfect hiding places for infantry, but any tanks breaking through the hedgerows were immediate targets. The allies eventually developed tools to deal with the hedgerows, such as rhino tanks and army sappers using copious amounts of explosives, but the terrain fundamentally hindered the type of fast armored warfare that was so effective in ww2.

I could go on about the struggles the allies faced in normandy, but I think this answers your question.

Sources: Antony Beevor "D-day: the battle for normandy"