Because this was the case for the last 10,000 years and you cannot change it overnight, unless you are in Soviet Russia and send people to Gulag for re-education. It is built into men's biological nature to be provider (like most mammals in the nature), you cannot change it because society decided less than a generation ago that this is no longer needed.
And also because many, if not most women are still expecting men to be the provider. Biology dictates that women need a provider (resources and security) to bring a child to this world and that provider should not be the government (which destroys the idea of family and the society with it).