The specific receptors the virus needs are in greater number at the back of the throat so the virus habitats there more on mass therfore the odds of catching enough covid on the single swab to gain a solid result when it's rna is amplified is higher.....the mouth testing is less accurate due to the low numbers of floating around virus overall earlier on in the infection....the back of the throat will catch more covid cases and earlier...
the premier was probably too chicken to go the other route on camera but if that is the procedure they are using and lots of places are, then so be it.
