You’re ignoring that they have the power to do so, they just don’t have the will. We have built mega projects before and taken land for it. This would be no different
The pertinent text is
>Early cases also reflected the understanding that state property was not immune from the exercise of delegated federal eminent domain power. See Stockton v. Baltimore & N. Y. R. Co., 32 F. 9 (Bradley, Cir. J.). The contrary position—that a federal delegatee could not condemn a State’s land without the State’s consent—would give rise to the “dilemma of requiring the consent of the state” in virtually every infrastructure project authorized by the Federal Government.
It literally calls out that major infrastructure projects would not have been feasible without this power