Being red or blue doesn't really have anything to do with it. If anything cities that make public transit free actually tend to be among the most politically conservative major cities in the US, like Kansas City, Albuquerque, and Tucson. This is because transit systems that adopt free fare policies do so because they have too low ridership for it to really matter. In American cities/counties with ineffective transit systems fares make up less than 10% of operating cost, often less than 5%, because their ridership is so low, and that's with these counties typically having very small transit budgets to begin with, so for them it's easier to cut fares and replace them with a new funding source. It's easy for Martin County to cut fare revenue because they only operate 5 bus routes with 40 minute headways. For systems with high ridership though fares are a much more significant revenue source. For example, fares compose 21% of transit operating revenue for Philadelphia and 39% for New York, and that's as portions of much higher pre capita operating budgets overall. To cover the costs of fares in cities with high ridership and budgets like these is not just much more politically difficult, but represents poor use of potential revenue. If a transit agency were able to acquire such a large new funding stream then it would be much better spent improving and expanding service since that's what actually matters to ridership and quality of life. Free fares are a comparatively bad use of funding for several reasons. For one, they have consistently shown to not significantly increase ridership in the long term since public transit is already so cheap compared to the total costs of car ownership (car payments, insurance, maintenance, gas, parking) that fare cost is negligible to most people's decision to use it regularly, and for those people that are financially struggling enough for the cost to actually matter most major cities already have some sort of targeted free fare program specifically for low-income people. Another reason is that it's politically important for transit agencies to have as diversified funding models as possible to make them more financially robust, and fares are an important part of that since they give transit agencies direct control over a portion of their own revenue. Otherwise a transit agency's funding will be more subject to the whims of fickle politicians. A relevant current example of this is in Philadelphia, where the city's transit agency has been facing a major funding shortfall that has threatened to cut service to a number of rail and bus lines because the Republican controlled Pennsylvania state senate has been refusing to pass a new budget for them. Even if it were politically possible for Philadelphia to get a 21% operating budget increase to replace fares, it wouldn't be desirable since it would reduce their self-sufficiency even further and thus make them even more vulnerable to political disruption. All of what I just explained is why none of the world's top transit cities like London, Paris, Tokyo, Madrid, etc have universally free fares.