"Some reason" here is: backwards compatibility. Good old Windows backward compatibility. If you've got habits or automations based on the Menu key (or its even

"Some reason" here is: backwards compatibility. Good old Windows backward compatibility. If you've got habits or automations based on the Menu key (or its even older shortcut: Shift+F10), Microsoft seems hesitant to break them, even if they felt they could change the default behavior of mouse users.