It does seem like there is an upper bound on Starlink's success given that terrestrial gigabit fiber exists in major markets. Maybe they have a plan for this?
Starlink was never designed to compete with terrestrial internet in any way.
If you have access to good high speed internet already then Starlink is not for you.
You are then left with all the exceptions to those general rules and I'm not sure that's enough to cover the very expensive cost of the platform.