Bicycles don’t need that, and it wasn’t made for them, so I don’t know why you’d charge “road cost” to the bicycle ledger when they’re such a distant second (at best) citizen on most roadways anyway.

Roads were originally paved for bicycles, before cars. https://www.cyclinguk.org/cycle/roads-built-cars https://www.theguardian.com/environment/bike-blog/2013/apr/1... https://roadswerenotbuiltforcars.com/

Maybe some roads somewhere were built for bicyclists, but I don't think you can generally say that when there are literally 6000 year old paved roads leading to Ur. Horse drawn carriages and wagons would benefit from roads and were probably much more common and important to business/transport than bicycles until the 20th century.

And what percentage of roads paved today do you suspect were done so primarily for the benefit of bicyclists?

The real cost is in the repaving and that's much more a property of weight of the vehicles. Bike infrastructure is significantly cheaper to create and maintain compared to nearly any other vehicle.

Sure we should, but that’s the case for all transport modes. Remember that you can just pave the smaller amount of space needed for cycling down a street and not a full-width road. A cycle track uses less pavement than a roadway thanks to being narrower, and probably lasts longer too due to less damage from heavy vehicles.

And doesn’t need to be built to the same standard of strength as a roadway that must carry trucks etc. In fact a dirt path is enough for a bike.

It is but it's a lot less comfortable to ride on, and that makes a difference for longer distances. (They also have the unpleasant tendency to become mud when it rains.) But ultimately sure you can usually get around on a dirt path.