Because Art one states specifically the reasons for the federal government to own land. Its A specific clause which modifies any general clause. You argument boils down to negating the specific in favor of the general.
Like Arguing the enabling clause for General Welfare negates the specific limitations of the enumerated powers.
It specifies reasons why the federal government may obtain land from the states with the consent of the state legislatures. But there is nothing in the language that limits it to that. For example, there would be nothing preventing the federal government from obtaining land for a federal park or an interstate highway or a weather radar site. What that section does make clear is that any property obtained from the states in controlled by Congress alone.
You argument boils down to negating the specific in favor of the general.
Because there is nothing that limits it to specific terms.
Like Arguing the enabling clause for General Welfare negates the specific limitations of the enumerated powers.
Is it your opinion that the Air Force, NASA, the U.S. Weather Service, the Air Traffic Control system, the Food Safety inspectors of the Ag Department are all illegal organizations as well?