When the Founders bound the former colonies together into one nation by writing the Constitution, they made an important choice. They decided to focus on powers with regard to this new government. Therefore, they granted the federal government specific, enumerated powers. In the 10th amendment to the Constitution, they granted all remaining powers to the states and citizenry. They didnt grant the states any rights, just powers. States dont have rights, only the powers allowed to them by their citizens.
The powers not granted to the national government by the States are retained by the States. They were not "granted" to the States by the Founders. While the Founders were the authors of the Constitution, and the architects of the Republic, they did not themselves bind the States to the national government. The States did that themselves, by the process of ratification.
The States themselves brought all the powers to the table, and agreed to a transfer of a very few and specific powers to the national government. The Tenth Amendment grants nothing, it merely clarifies for the conveniently confused what should be intuitive - that any powers not enumerated were not granted, but retained.
I updated the post, thank you for highlighting that unclear wording.