I have seen many public transport systems privatised and worsened over time; since there are many ways to play with funding and quality, you can hide a whole lot of bullshit. Frequency, hours, cleaning, security, ticket price, and maintenance... It can be unclear why a service is declining or who is accountable. That's what I mean by easier to understand.

Roads are public in a way that introducing a toll on an existing road is not politically viable, and maintenance issues are easier to spot.