Or the other way round: why should telcos sink billions into covering rural areas with extremely low population density where they'll never be able to recoup costs even closely? They're not having any incentive to do so now, they'll have even less once Starlink is up and running because half the target customers will be happy with that.

That is why basic telecommunication infrastructure should be built out by the government, similar to roads, sewers/drinking water/gas pipes and postal service. Letting private companies do the job without mandating equal service will always lead to rural areas being dropped off the radar, and besides it's an enormous waste of resources if two or more service providers have to dig up half the country to bury infrastructure.