Why did HMS Renown carry so many Oerlikons?

Why was HMS Renown fitted with many 20-millimeter Oerlikons instead of more medium 40-millimeter weapons?

The lighter weapons better matched the weight limits of available positions and could be fitted quickly from equipment already in supply.

Adding antiaircraft weapons was constrained by where a ship could safely carry their weight. Oerlikons could occupy positions that would not support heavier 40-millimeter mountings. They were also available through the existing supply system and could be installed quickly. Renown's fit therefore reflects practical wartime refit constraints rather than a simple preference for smaller-caliber guns.