Treaties of the time dealt with relationships between countries, the rights and privileges that one country’s citizens would have while in another or while dealing with another. They did not reach into the internal matters of a country and mess with natural resource use, labor, manufacture, endangered species, migratory birds, air quality, climate change, transportation and every aspect of commerce.
Quite true. But even in such terms, a treaty could not impose any unconstitutional burden on the Union or any State.