Probably because the HQ was basically a full US design, and the WA was the Aussie modified version due out around 1974-5. It got delayed and the HJ, then HX and HZ were released. My guess is the WA dash was then used in the HJ. The WA got canned and the WB was released once they realised that passenger versions of the WA or WB Holden were never to be built.

If anyone gets a chance to look inside and under the bonnet of the WA Kingswood at Birdwood it'd be interesting to see what dash is in it and what the ID plates say.