Using the Licensing Tool (LT), I chose an OU (parent OU), and it forces me to also license all sub-OUs (children OUs). Why?

When an OU is selected at any level, all OUs within it are automatically selected and cannot be un-selected. This is because you’re licensing from this OU “onward.” This enables you to create new sub (child) OUs within the parent at any time during the year.

That being said, there is no way to exclude a child OU from a parent, because you’re licensing that parent OU “onward / downward.”