You need to rephrase that to "This is really really not normal in white anglocentric cultures"
I personally find it really abnormal that people spend 5 minutes in the shower and wash themselves with their hand. How can you wash thoroughly in 5 minutes, with no cloth? You can't.
Lots of people from lots of cultures follow a similar, if not more thorough hygiene routine. It's the norm in African and Caribbean cultures to be very clean. Anyone I know from an African or Caribbean culture is this clean if not cleaner.
I'm not personally obsessive about it and other than feeling a bit gross, I can carry on with life if I can't get a shower for whatever reason.
Anyway. It's recommended to do deep exfoliation once a week by most dermatologists across the board.
Double shampooing hair is again recommended by the majority of hairdressers.
Also I'm curious - how much exactly do you know about the upkeep of afro textured hair? I'm guessing you don't know a lot, if anything.
Because if you did you would know that afro texture hair requires specific upkeep to keep it healthy and stop it snapping off. Our hair texture is much drier. It also gets "dusty" because it picks up fluff and fibres from the environment. I need to scrub my scalp to loosen it and wash it off, along with the leave in conditioner or oil from earlier that week. If you googled you'd know this.
My daughter also has a similar texture hair. Would it make you feel better if I ignored her needs, and didn't regularly moisturise her hair because you think that level of self care is abnormal? No doubt you'd be on here writing a post titled "AIBU for assuming a child was neglected and calling social services" if you saw her walking down the street with her hair uncared for, because I can't win with people like you who seem to pride themselves in their ignorance of other cultures that reside in the UK.
Just because something isn't done in your culture doesn't make it inherently abnormal.
Oh and I'm doing plenty of favours teaching my daughter to have good personal hygiene thanks.