MM wave distance might surprise you. Dense foliage can be a problem but in the 80s my company was testing some stuff in the 50GHz range and over a 10km path we had huge signals sticking 30dB out of the noise floor of a spectrum analyzer. This was using tiny horn antennas about 3in long at each end.
But those areas already have broadband - they already have cable or fiber - and the telecom people just continue to pour money into those areas. Why? Are they that allergic to running new cable to areas it's never been run before?
Millimeter wavelengths in 5G won't work in rural areas. You have to have a direct line of sight and it's going to have to cover significant distances. But again, they like to focus on 5G, and cell tower upgrades in general, in places where cell coverage is always great. Not to mention the absurdly low monthly data allotments on cellular plans.
Sorry... I'm drifting this thread off topic. This is just a soapbox issue for me.