Why do governments fulfill some of society's needs such as education health-care or mass transit?

Some governments fulfill some of society's needs such as education, health care, and mass transit so that all members of the society can participate. These are public services and the private sector doesn't always provide them. It is often not profitable for the private sector to provide these services, so governments step in. For example, some bus routes might not have enough passengers to make a profit, but people still need it. A company won't want to run a loss making service, so the government does it instead, or will at least subsidise the service to encourage private operators to do it.