I know in the US people obsess about squeaky clean hair.
In India, I have seen women with long lustrous black thick hair and wash just once a week.
I for one, growing up had very thick hair, it is curly though, and had never used shampoo till I was about 15. Once a week my mom would give me a coconut oil massage , I would leave the oil on my hair for about1-2 hours and wash off with a paste of gram flour.
But then I went to college and was swimming competitively, so I started shampooing regularly to get the chlorine off, I lost a ton of hair.
I have gone back to oiling my hair with coconut oil once a week and using a silicon free shampoo and for 5 days out of 7 my hair looks good.
I do not use soaps to take a shower, I sometimes use it on my feet and underarms as I tend to get sweaty there, but this is rare.