"Of course, nobody really LIVES in most of those huge data voids, ..."
Yes, because farmers don't need to call 911 for help in an emergency, call the local food co-op to check this week's prices, order new seed from a supplier's web site, or e-mail the mechanic to get an ETA as to when the tractor will be fixed. And we certainly don't want the farmer's kids getting a decent education via distance learning web sites, or talking to their friends in nearby cities.
Putting cell towers in those areas is not profitable, but it is necessary. I say this as an Australian - for over a decade the commercial carriers did squat to wire up the country-side. The Australian government had to create its own carrier from scratch because the free market just didn't care about the 95% of the country where "nobody really lives there". Oh, except for the people who do.