Selectively intuitive setuid behavior

In my mediocre, pre-'90s universe, we use `setuid` to ascertain that _we may drop privileges_ **after** binding the socket.
This is necessary, as _one does not simply_ bind a port below 1025 without doing so as root.
_In fact, that is the sole reason to run such stuff as root._

However, when set (left) as such, the software attempts to drop its privileges _as soon as it evaluates the arguments_.

To me, this makes somewhat limited sense.

Am I missing something?
I would be glad to receive some pointers.