A lot of discussion about Semmelweis, but the actual reasons:
"Some factors that hindered hand-washing were days with busy workload and a feeling of not being watched.
A World Health Organization (WHO) report has also listed other barriers to adherence with hand-washing guidelines, including:
Working in the ICU, surgical unit, or emergency rooms
being a nursing assistant (rather than a nurse), or physical therapist
Sinks are inconveniently located/shortage of sinks
Lack of soap and paper towels
Male sex
Handwashing agents cause irritation and dryness
Understaffing and overcrowding
Wearing gloves and the belief that using gloves avoids the need for hand hygiene
Not thinking about it/forgetfulness
No role model from colleagues or superiors
Skepticism regarding the value of hand hygiene
Disagreement with the recommendations"