Just speculating here, but maybe because of false positives where flu cases get labeled as Covid? I've heard that PCR tests were not meant to be used for large scale virus detection.
EDIT: The PCR test quote was fact checked and deemed to be misleading, but it still sounds like they are not very accurate [0].
EDIT: The PCR test quote was fact checked and deemed to be misleading, but it still sounds like they are not very accurate [0].
[0]: https://www.reuters.com/article/uk-factcheck-pcr-idUSKBN2442...