Read the wiki link. [1]

The goal was to have a globally competitive merchant marine based on a home grown ship building industry to call on in case of war. Trying to balance both sides.

The end result is that that home grown ship building industry has all but disappeared together with the educated population required to crew it.

[1]; https://en.m.wikipedia.org/wiki/Merchant_Marine_Act_of_1920

Your argument is post hoc ergo propter hoc. But as with car import tariffs and quotas, nobody doubts that removing all import obstacles would lead to the offshoring of most remaining car manufacturing.

What economists argue that the Jones Act is suppressing is greater use of domestic sea transport, which could be much cheaper than trains and trucks. Without the Jones Act sea transport would grow, but undoubtedly using foreign ships, perhaps relying on a primarily foreign crew. OTOH, a much larger domestic shipping industry would likely spur demand for downstream services, as well as open up opportunities for growth elsewhere in the economy, so overall jobs for Americans might grow. But deregulation grow the ship building industry domestically? Nobody expects that.

Globalization, not the Jones act made it disappear.

If you want to bring it back, you have to deglobalize. (Good luck with that!)