The Crazy Horse monument was not begun or sculpted by Gutsun Borglum. It was begun by Korczak Ziolkowski and commissioned by Lakota leader Henry Standing Bear. Ziolkowski's heirs have continued the project since his death.
Gutson Borglum was the chief carver and artist on the Mt Rushmore project as well as the original Stone Mountain project near Atlanta.
The reason that it is still not finished and Mt Rushmore is has to do with federal money. Crazy Horse has been carved solely from private donations while Mt Rushmore was carved with Federal funds
Mt Rushmore was never fully complete, however after work was halted due to WW2 it was finally considered completed by congress MANY years later and finally dedicated some time in the mid-1990's.