Sweden is about the same size as California but with about one third of its population (and about 2/3 of the population density of US), still it is in the top 10 internet access list in about every metric you can think of (together with for example Norway and Iceland, neither especially densely populated) so I don't think the density argument holds.
Stockholm and LA are excellent examples. In Stockholm, there is a municipally owned company that builds fiber. It received no government funding, and built the fiber over more than 15 years in a demand driven way (building first to businesses, then to places with highst demand). It leases access to ISPs, and there are no mechanisms to force it to subsidize lower income or disadvantaged people.
Contrast Los Angeles. There, Stokab’s business model would be illegal. Builiding out based on demand might mean that wealthier neighborhoods would get fiber a decade before poorer neighborhoods. Disproportionately, white residents would get fiber before hispanic residents. That would be politically untenable (and would be completely impossible to put the government’s imprimpteur behind such an effoet as with Stokab). For that reason, most US cities make Stokab’s business model illegal.
Los Angeles had a fiber proposal: https://www.wired.com/2013/11/la-fiber. It tried to get companies to build a fiber network. By contrast with Stockholm’s approach, neighborhood income and population density could not be a “factor” in the rollout. That means that any ISP would have to build to new neighborhoods that were not economically justifiable. The ISP moreover would have to provide a minimum level of free access to all residents. It would thus have to recover the cost of that from other residents, driving the price higher and decreasing the competitiveness of the product. Unsurprisingly, nobody took up Los Angeles on that proposal. Nobody would build it, it made no business sense.
In Stockholm, fiber was a simple business proposition, built with private capital. In California, it was a social justice initiative, unattractive to private capital. Which is not necessarily itself a problem, but if you want to do that you need to be willing to build it with public money.
Also, New Jersey is about as dense as many European countries that have great broadband and competition--yet New Jersey has crappy broadband. So, it's not due to USA's low population density.
6 years ago in Jersey City I had Fios, while across the river in Manhattan, it was very difficult to get. In my part of New Jersey in 2012, I had far better internet than I did in 2018 France — and much cheaper.
Sure, Swedish cities are a little less sprawly than American cities of the same size (I have no data on this but my general experience is that both apartments and houses a slightly larger in Sweden but a bigger part of the housing stock is in apartments), but I still don't think the geographical explanation holds especially in densely populated regions like the Bay Area.
I think it has more to do a lack of interest from US politicians.
The Bay Area isn’t densely populated. San Jose to San Francisco is mostly single family homes in suburban neighborhoods. Even the “dense” parts don’t hold a candle to East Coast cities.
