Earlier quoted context omitted.
This happened with trains in the 19th century and it was an absolute disaster. Please learn your history on privatized public goods. It results in massive fragmentation in standards, extreme levels of corruption and an overall worse experience for most people.
We know about the downsides now. For example, the New York system was private and actually paid for itself. New York subsidized the system. Now it's inefficient, poorly maintained, and expensive due to excessive salaries. https://www.youtube.com/watch?v=hPhC3-9mSb4
That is not to say you can't have private systems that work (Tokyo, Hong Kong). New York just isn't a particularly good example.