Growing up in Toronto, I always assumed that public transit just provides transportation and nothing more. Their income comes from tickets and from government subsidies.
In areas of the world where profitable private mass transit exists, the transit company also deals in real estate. They own land near stations before construction and either rent it out or sell it. They build and own malls on popular stations. This is a large reason why financially sustainable private transit companies exist. This is also known as value capture.
The upside to private transit companies is that it is not a political debate about how much to subsidize them - they are self-funding.