You're saying public transport is on the same level as roads. Most roads are free to use because they're maintained with tax money, just like free public transport would be, because they're both in the public's interest.
[1] Both because there are higher safety expectations for railways than for roads and because one of the inherent working principles of railways is to bundle individual demand into larger units (a.k.a. trains) that can be moved across the network en bloc. If everybody tried to operate their own individual little train across the network the way you do with driving your car, things wouldn't work out.