Why is ASA 8-2-D written this way?

[Dakota]

A question on the Fed board got me looking at this.

ASA 8-2-D

Section 2. BATTER-RUNNER IS OUT.
D. When the batter-runner fails to advance to first base and enters the team area after ... a hit batter (Fast Pitch)...
EXCEPTION: ...(Fast Pitch) on a hit batter. The batter-runner is not out...

Consider the case of a hit batter in the fast pitch game. This rule says the batter-runner is out if she enters the team area and then lists an exception that says she is not out.

Why not just leave hit batter out of the rule in the first place?

I must be missing something.