You need a cell tower every 20 miles or so, less for a performant one. There's not dark fiber at that density in remote regions (remote is, by definition, lacking infrastructure). There's a better chance of power, and for the cases there's not, solar/battery is fine for a cell tower, especially one designed for lower power remote installations.
The initial cost for a dark fibre on a power pool is very low and can give you low latency and high bandwidth.
Starlink antenna needs a lot more energy and has a high montly cost.