I think you (and probably the author) have got this exactly backwards. Sprawl creates blight when the rate of building outpaces the needs of population growth. The evil sprawlsters are creating new costs, but they aren't subsidizing old roads. The sprawl usually happens outside of long-ago drawn city borders, anyway.

If you have 5 families living in 5 houses in the urban core and you build 5 new houses for them to live in out in the suburbs, then population needs to double for there to be full occupancy.

As a case study, take a look at my home town of St. Louis. Much has been made about the city's population loss. But that's just in the urban core; the region's population has actually grown slightly over the last 40 years. It just hasn't grown fast enough to fill up all the new houses we've built out across the river.

The sprawlsters aren't subsidizing the old roads. They have completely abandoned them and are leaving them to nature.