A treaty is much easier to ratify than a Constitutional amendment. According to Article 2, Section 2, Paragraph 2 of the Constitution, it only takes the President's signature and two-thirds of the Senators present to make a treaty part of the supreme law of the land. The House of Representatives, who speaks most directly for the people, has no say. The states, who delegated a portion of their authority to the Federal government by ratifying the Constitution, have no say. A stroke of the pen, and a quick vote, and the treaty is the law of the land.
Treaties are often massive in size, and yet leave many details unspecified.
This is where we need to recall the lesson learned by the unfortunate farmers who traded their mineral rights for some quick cash. This is especially true since the ratification process for a treaty requires far less public scrutiny than the ratification process for a Constitutional amendment. A stroke of the pen, and a quick vote, and the treaty is the law of the land. So now you are thinking to yourself, that guy is one of those conspiracy nuts or some protectionist-isolationist Neanderthal. In exchange we get to force the Europeans to buy our food products that contain additives that the European Union does not like.