> why didnt the roads collapse into a state of disrepair which no one was willing to pay for?
A street in disrepair is still usable, a street car line in disrepair becomes unusable much faster. Only one part of the rail needs to fall apart when nobody will pay to fix it and you can't use it anymore. Potholes and washouts and lots more problems are solved by driving slowly and carefully. Especially with earlier automobiles which were more likely to run on dirt roads.
This is a plausible hypothesis, but the thing that's missing is how many times can rail be traversed before being unusable and how many times can a road be traversed by the same measure. Intuitively, I would imagine the net tonnage passed before wearing out asphalt is far lower than it is for a chunk of steel welded to the ground. Maybe the cost of maintaining rail feels worse / is a harder political sell because the full price is acutely concentrated in time, whereas each individual pothole is a mere budgetary papercut?
A street in disrepair is still usable, a street car line in disrepair becomes unusable much faster. Only one part of the rail needs to fall apart when nobody will pay to fix it and you can't use it anymore. Potholes and washouts and lots more problems are solved by driving slowly and carefully. Especially with earlier automobiles which were more likely to run on dirt roads.