> I might understand this incorrectly, but doesn't it also mean that American businesses have a greater market to sell to?

"American" companies aren't always entirely owned by Americans. Sometimes they get purchased outright by foreign conglomerates or shareholders (eg. Anheuser-Busch) or take on foreign investment (eg. SoftBank). Once they're public, lots of entities can own the stock.

Labor doesn't have to be based in the US. Wages go overseas all the time. Your iPhone is manufactured abroad. Amazon hires lots of non-American programmers.

Companies move to states with fewer labor laws and cheaper labor also.

Is the only difference here that there is a possibility of federal tax revenue being distributed throughout one country? You can even go one more level down to cities and states rather than states and country.

Minimum wage is closer, environmental standards are somewhat similar, and laws can be passed on a federal level. It is just as easy for workers to change states as businesses while internationally it is easier for businesses to change locations than workers.