Those are microwave which basically need line of sight? I was thinking of lower frequencies which can sometimes go hundreds of kilometers without repeaters.
Bandiwdth, mostly.
The lower you go in frequency, the less bandwidth is available.
The entire "HF" spectrum is ~30 MHz. My Wi-Fi at home uses a wider channel than that.
The lower frequencies -- that will travel across the ocean, unaided -- don't have anywhere near the bandwidth necessary (to support the throughput that they need).
They are. See mshook's response, with nice reference links downthread: https://news.ycombinator.com/item?id=16196339