Different strokes for different folks.

There are at least some public forums, where if you want to speak, you just join the line, and if there is time permitting,
you get to speak.

The APS board requires that you sign up before the meeting
and enforces that rule vigorously.

I can only suppose that it limits the number of people who
can speak, and specifically to those who can get off of their
work early enough to sign up.

If there is a good and ethical reason, it escapes me.