I don't understand the reasons, but in 1941, the British Royal Navy was an extremely proficient and professional service, while the British army had serious problems. There are many potential explanations. There was the friction between the regular British army and the British Indian Army. Many of the commanders in 1940 to 1941 were Indian army trained. There was also the obtuse influence of the mechanization clique in the British army. They thought that they were trying to modernize the army, but they didn't understand how tanks and armoured cars were best employed. The German army had a good understanding and doctrine and they beat everyone in their path up through the end of 1941, although Russia was proving to be too much for them. The Australian and New Zealander commanders and men were much better prepared for war than the British. On the other hand, the British forces in North Africa in 1940 to early 1941 were trained to a very good state and were well led. Their reward was to be dismantled by General Wavell.
I have never liked Bernard Law Montgomery, but I have come to appreciate what he accomplished. He took the British and Commonwealth forces in the Mediterranean theater and reformed them into a force that could win battles. He really did not have time to make the transformation prior to the Second Alamein, so they had a much harder time than a Montgomery army would have in 1943 or 1944.