Why did British forces at Sword Beach fail to link up with Canadian forces from Juno Beach on D-Day?

On D-Day, British forces at Sword Beach and Canadian forces at Juno Beach failed to link up by the end of the day, leaving a 3-km (2-mile) gap between their positions.12

This failure was primarily due to the intense resistance encountered by the Allied forces and a significant German counterattack. Specifically, elements of the German 21st Panzer Division launched a counteroffensive into the space between the British 3rd and Canadian 3rd divisions. While the Canadian forces had been tasked with establishing a joint beachhead with the British, they faced heavy casualties from beach obstacles and unsuppressed German strongpoints, which hindered their progress toward the east.314

The German counterattack, which included panzers and mechanized infantry, reached the coast by 20:00 hours, though it was eventually halted by Allied antitank weapons, air strikes, and tanks. The two forces were not able to successfully connect until June 7, when the commandos pushed through the remaining German defenses at Luc-sur-Mer.324