Southwest Free Preferred Seat Question/Confusion

I was booking a flight for August and I have the Southwest RR Perf Biz, which says "Complimentary Preferred seat at booking" (when available) - but when i go to choose a seat, it still shows a charge for preferred seats. I assume that means they're all taken for that flight?

I tried adding the preferred seats to see it if would give me an instant discount once in the cart, and then also tried to upgrade after booking, no luck.