The whole point of building a cellular network is the ability to run low power devices (handsets), using directional antennas on the cell sites, to allow the repeated reuse of a limited number of frequencies across a geographic area.
I could build a network using high power repeaters on mountaintops, but that would burn through the available frequencies in a big hurry, while only serving a relatively small number of subscribers at a time.
Some systems, such as Nextel, actually have high level sites, and are not as built out as Verizon, AT&T, Sprint, or T-Mobile.
Look back at the old IMTS telephone networks, which had a very limited number of channels (11 VHF, 12 UHF), and high level sites, covering large areas (40-60 miles in diameter). There were waiting lists for service, with expected wait times in some metro areas measured in years. Imagine having to put your name on a list, and 5-10 years down the road, finally being told that next year you might be able to get a mobile phone. Of course, at the time, a "portable" phone meant a briefcase, weighing 20-30 lbs, and most folks who had mobile phones, had them installed in their car/truck, with a briefcase sized radio deck in the trunk, and a control head with a dial and handset on the dash (or in the rear section of a limo).
There were other systems, mostly operator assisted, but some of which operated similar to a amateur radio autopatch, with either selective calling of a individual subscriber radio, or in some cases, a pager was used to alert users of a incoming call. (they page you, you call them.) airtime prices were high, up to several dollars a minute.
