Starship makes space access 1000x cheaper than before, with cost-to-orbit under $10 / kilogram. Also much larger payloads become possible. That's an insane economic unlock, because space contains unlimited amounts of resources and energy. Space-based manufacturing, building space hotels, mining asteroids etc. becomes viable. Larger satellites and probes for commercial or scientific use becomes possible.

All this might not make sense in a standard business sense. Real profits might be decades away, who knows. Anyway, people are willing to throw their money at it, because they think it's important.

If they succeed in the long term, it'll easily be the most valuable company on Earth.