P.S. Another reason why Macbeth might have more injuries than either Hamlet or Romeo and Juliet is the setting. In both Romeo and Juliet and in Hamlet they're fencing with rapiers, appropriately to the setting. But in Macbeth they're in the Scottish highlands, and a rapier just wouldn't look right. I don't believe Shakespeare ever explicitly specified what kinds of swords the characters in Macbeth are fighting with, but traditionally they've used either longswords (two-handed) or arming swords (one-handed swords, which are what you might think "longsword" means if you came to your knowledge of weaponry through D&D or other RPGs). Both of which are heavier (especially the longswords) than a rapier, and easier to accidentally injure your opponent with (broken bones, concussions, etc) than a blunted stage rapier.

So that fact alone might help explain why injuries tend to be higher in stage productions of Macbeth. It's just inherently more dangerous to perform than the rest of Shakespeare's plays.