Just don't have the time or energy apparently.

"The NHS advises that to maintain a basic level of hygiene, a person must wash their face and brush their teeth daily; clean their hands after using the toilet; wash their genital and anal area each day; and fully bath or shower at least twice a week."

http://www.independent.co.uk/life-style/health-and-families/health-news/majority-of-uk-women-dont-bath-or-shower-10065854.html