The Black Hills were stolen by our government:
"The Great Sioux Reservation, including the Black Hills, was "set apart for the absolute and undisturbed use and occupation of the Indians"[in the Fort Laramie Treaty of April 29, 1868. Those treaties were not upheld by the United States, and the Sioux Nation was eventually forcibly removed. The Supreme Court ruled in 1980 (US v Sioux Nation) that the Sioux Nation never received just compensation for their land, writing "a more ripe and rank case of dishonorable dealings will never, in all probability, be found in our history." The Court concluded that Congress had failed to "makes a good faith effort to give the Indians the full value of the land." The Court ordered "just compensation to the Sioux Nation, and that obligation, including an award of interest, must now, at last, be paid." However, the Sioux Nation refused the monetary award, stating that their goal was return of the land."
They also blackmailed the Sioux:
"United States illegally seized the land and nullified the treaty with the Indian Appropriations Bill of 1876, without the tribe's consent. That bill "denied the Sioux all further appropriation and treaty-guaranteed annuities" until they gave up the Black Hills."
https://en.wikipedia.org/wiki/Seizure_of_the_Black_Hills
The Black Hills are actually sacred to several tribes. They don't want the $billion+ settlement the Supreme Court gave them--they want their stolen land back! trump's statue will be the latest slap in the face, like the insult of Mt. Rushmore.