Multiple issues
1. The higher the frequency, the shorter the wavelength and the poorer the indoor reception. For this reason, through-the-wall relays have always been recommended if you want good indoor reception - but don't expect the telco to pay for that! A cheap domestic one can be nothing more than a passive waveguide or antenna-to-antenna cable, the upcoming modern equivalent being VoIP over a WiFi-to-broadband router.
2. The higher the frequency the greater the data capacity, hence loved by every new generation. This tends to make newer generations less indoor-friendly than older ones.
3. Cost-benefit to the supplier: why give a **** about your users and install more cells unless your competitors do or the regulator makes you?
4. Cost-benefit to the user: why install obsolescent toys when you can just make sure that both your phone and router have WiFi and your telco supports VoIP?
So really, everybody is to blame: cheeseparing suppliers, irresponsible regulators, lazy consumers and the economics of progress.
Biting the hand that feeds IT
