Part of the reason this type of network isn't already built, is likely most folks living in very remote places simply don't need or want 1Gbps internet (or even DSL) - or at least don't know they want it.
There are folks with dial-up connections still, unfortunately, and not always because they have no other option. The more technically-inclined people here on HN wanting to work remotely and stream multiple 4k videos at once - they aren't majority of, say, AT&T's customer base. AT&T won't build this out if they think 1 in 100 potential customers will actually upgrade.
This will change over time, as a generation of folks that grew up with technology age and move into more rural areas. Hopefully demand will drive these network upgrades over time, and make it make financial sense to run new fiber in rural areas.
This could even be expedited with some sort of National Infrastructure Bill to fund it today, subsidized by tax payers since the benefits are ultimately so great.
I still think that's ultimately the better (and long term, cheaper) option verse thousands of satellites being launched every few years.