Again, because it’s completely irrelevant to to the shailah being asked. No one is actually doing it. We are just trying to determine a halacha.
See the חק נתן on דף יט.

Spent time over Shabbos looking things up, I'll give you the חק נתן
Bemichilas k'vod hamechaber, The מקדש דוד does
not speak about payos, ר' אהרן לייב when he brings the מקדש דוד says ואין לומר ... דמסתמא היו צריכין לגלחן.
Why is it only מסתמא? The שמועת חיים on the מקדש דוד learns that payos
are biseder.
ר' איסר זלמן is only mechalek between פרוע ראש of a kohen and a zar, I only see a mashmous if you are making a hanocha.
Though I was thinking (possibly this is the machlokes) the questions that have to be asked are
1. What is the geder of פרוע ראש. Meaning, a Kohen has to cut his hair every thirty days so as not to be, but at what length 0,2, or as long as he has a haircut and can be 5 feet long?
The מנ"ח קמ"א has a מח' תוס' ורמב"ם possibly תלוי on how to learn, as there is also מח' how to learn the רמב"ם