Why do we always see "Men at Work" board but no "Women at Work" board?

This is a subject highly argumented in between men and women. Men says that it is because men everywhere does the 'real job' and women are lazy and cannot perform as much as men does. Even if women work as consultants or similar jobs at these areas, it is always 'Men at Work'. On the other hand, women thinks that this statement is 'sexist' and discriminating. Womens' justification on this is that they are the hard workers at home looking after the children, which is considered as the hardest job in the world.
The fact is that the purpose of Men at Work board is to caution everyone around that physical and dangerous jobs are being performed at the location where this board is being placed. The board is usually used at construction areas, where over 99% workers are men.
men at work