Starlink is presumed to be the main moneymaker which could justify a much higher valuation than 100B if their plans pan out
There’s also quite a lot of opportunity of Starship is successfully “fully and rapidly reusable”. Point to point transport of cargo and potentially even humans, etc.
Falcon 9 already launches more than 50% of all Payload sent to orbit today.
They will have the launch airline or cargo service company too not just build starship and get regulatory approvals, promote, sell tickets/capacity and provide customer service etc.
All risky steps in a possible side use case for the starship program. Realistically none of this happening before mars missions start likely 2030s.