Well if you make the argument that it will replace terrestrial networks and that's why its worth X trillion $ then yes, you do actually need to cover the 1% of earth surface where the waste majority of people actually spend most of their time.
The question is not if its a good business, the question if its a 2 trillion $ business, and if you only cover the 95% of earth without coverage. That more like a couple 100 billion $ business at best.
I never said it would replace terrestrial networks... you invented that claim yourself and are responding to a strawman.
Starlink mobile is for rural areas, and the other 90% of the planet that's not well served by traditional terrestrial networks.
And 40% of earth's population live in rural areas, so there is a large market for this kind of service.