Why do police ladies get buzz cuts?

Because its practical.

Even though there are no strict rules on the women cutting their hair, Buzz cuts are the most practical.

The female officer will be expected to do the same roles as a male officer, some of these are physical ie chasing suspects, restaining etc.

With long hair even if tied back can come loose the officer doesn't want to be retying a bun while in pursuit.

Also if a suspect fights back long hair can be grabbed, pulled and used against the officer, a buzz cut there is no length to grab.