The people who actually wrote the language of the 10th amendment, which was presumably someone in the 1st Congress.
The preamble originally listed the states by individual name, and the Committee on Style wasn't supposed to change the meaning of anything, just the wording.... so I'm not so sure the Preamble hasn't been used in ways that, again, wasn't originally intended. Just a thought. Obviously at this point, after centuries of legal rulings, "We the People" does refer to the people of the United States collectively, but I'm not sure that's what it was supposed to mean when written, unless Governeur Morris was being sneaky.
(Don't know if anyone here has responded to this since I haven't been through all 18 pages, but...)
According to Constitutional Scholar and Yale Professor Akhil Reed Amar, the wording was changed because they couldn't be sure which states would ratify the Constitution and join the Union. It seemed presumptuous to assume anything. See America's Constitution ~ A Biography ~