In case of Andrew Carnegie, it was probably desire at end of his life to been rembered as not only a ruthless businessmen and monopolist.

"Carnegie spent his last years as a philanthropist. From 1901 forward, public attention was turned from the shrewd business acumen which had enabled Carnegie to accumulate such a fortune, to the public-spirited way in which he devoted himself to using it on philanthropic projects."

https://en.wikipedia.org/wiki/Andrew_Carnegie

Bill Gates is in similar phase of life.