[JRandomFreeper]

Article 1 Section 8 describes the powers assigned to the federal government, and none of the powers assigned require owning vast territories within states.

If it's not allowed to the federal government specifically, then it is forbidden to the federal government, and reserved to the States or to the people.

/johnny

[Sherman Logan]

Your theory might fly a little better if you could point to a lot of 19th century claims that the federal government was prohibited from retaining ownership of land nobody wanted to buy.

I’ve never seen any such claims, but perhaps you can find them. Otherwise, AFAIK, your theory was not propounded till quite recently.

All of which is a quite different question from whether the government retaining such ownership is good policy.