there are many, but one main reason for hygiene is for example if some requires first aid due to a cut, the wound could be infected if people leave areas dirty or un clean. Plus its just normal practice blatatnly obvious why people should keep themeselves and their work environments clean.
because if someone is dirty, smelly etc it isn't fair on the people who have to work with that person and it also not nice for customers. It reflects badly on the company as well. I don't know of any employers who would knowingly employ someone with bad personal hygiene. Personal hygiene costs nothing apart from washing powder and a bar of soap so noones got an excuse really.
Theres no excuse for a smelly bum,or armpits its just lazy,Jump into the shower every morning and night and have a nice smelling crack.................