"Why were women marching?"
Well James, they had a reprieve from domestic duties and they just felt like it. You'll be surprised to learn that there were men marching with them. 
Why? Because we don't want to go back to when men could just grab what they wanted.  Many of us want to avoid kissing magnets. We don't want our daughters (or ourselves) being referred to as "pieces ofass". We want to have access to health care, including abortion. Some marched because we don't want our natural resources plundered for profit. We don't want to ignore climate change. We marched because we care about ourselves and one another - inclusively - and our planet. We marched with millions of people around the world because.... because We Can! 
We are not going to sit quietly while Chump rolls back decades of progress on civil rights and environmental protections.
Oops! The roast is done! I better get back to the kitchen!!