Because one of the things that was actually done at the time was a defender taking a FK, lifting the ball up to his teammate's head who headed it directly back to their GK.Tend to agree with you. But the question is (as pointed out in the above), why was "including from a free kick" added in the first place.
Lots of weird wordings and Laws are on the book because they actually happened.
Like the GK scoring an own goal on a CK. Explicitly called out because it happened somewhere.