[ZiiS]

You can build a small ship and a track record of profitable trade with the next port, then the next country over before undertaking an ocean crossing.

[munificent]

But you can't incrementally upgrade that ship to become a large ship.

At some point, you need the capital investment to build a big ship, and the return on that investment is zero unless you build the whole ship.

[tonymillion]

And by the time you've done that 97.3% of all shipping from the new world is being handled by a small handful of companies with gigantic cargo ships.

But congratulations, you've successfully created a small "local" business with a decent number of customers who are reasonably loyal. You should be happy with what you have and possibly invest in future generations who want to colonize the moon or something (assuming you want to expand your wealth)