Partly, the Gazala Battles were lost because Rommel pre-empted British action

While General Neil Ritchie's 8th Army was moving into position to attack, Rommel's mobile forces pre-empted British plans. Rommel's strike force consisted of the 21st Panzer Division, the 5th Panzer (formerly 5th Light Division), and the 90th Light Division. They went South around the British desert flank. They were aiming behind the British lines, including for the famous Sidi Rezegh airfield, Southeast of Tobruk. The first phase of the battle was unfolding on 27 and 28 May 1942. The speed and decisive movement unhinged the British command, and succeeded in bagging the divisional commander, General Frank Messervy, and disrupted the 4th Armoured Brigade. Things only got worse from there.