Most of the cost of laying fiber is passing a neighborhood. Fiber provides live and die by their uptake rate--the percentage of the houses they pass that actually subscribe. Build out requirements tank your uptake rate, because in most cities large segments of the population simply cannot afford to subscribe. If the provider is forced to build into those neighborhoods anyway, they have to raise prices everywhere else, which further reduces their uptake rate.
So think about that from a prospective competitor. Maybe 20% of the neighborhoods in say Baltimore would be willing to pay enough for fiber service for it to be worthwhile challenging Comcast in those areas. But if I'm forced to build out everywhere--in a city where a quarter of the population is below the poverty line--there's no chance it makes economic sense for me to do so. I'd have to raise prices so much in profitable neighborhoods that I'd never be able to compete with Comcast.
This is, by the way, why Baltimore city doesn't have FiOS despite being in the heart of Verizon's FiOS area. And it's also why nobody else will build fiber here either, despite the city desperately courting providers.
So think about that from a prospective competitor. Maybe 20% of the neighborhoods in say Baltimore would be willing to pay enough for fiber service for it to be worthwhile challenging Comcast in those areas. But if I'm forced to build out everywhere--in a city where a quarter of the population is below the poverty line--there's no chance it makes economic sense for me to do so. I'd have to raise prices so much in profitable neighborhoods that I'd never be able to compete with Comcast.
This is, by the way, why Baltimore city doesn't have FiOS despite being in the heart of Verizon's FiOS area. And it's also why nobody else will build fiber here either, despite the city desperately courting providers.