In the United States at least the subsidies for public transit pale in comparison to subsidies given to drivers in the form of road maintenance and parking subsidies. Subsidized public transit makes a ton of rational sense. The fewer cars there are driving around me the safer I am and the cleaner my air is. I want everyone to have an option to get around that doesn't require a huge upfront investment. It seems you and I are optimizing for different values but there are plenty of rational reasons to support it.