What is "materialistic" about inventing a motor capable of transforming the world, deciding that the world doesn't deserve it, and retiring to an extremely small, closed, primitive culture populated by similarly-minded people?
How is it not the "looters and moochers" who are the godless materialists, damning those who fled to avoid the inevitable confiscation or destruction by the majority?
Hank Rearden is forced by law to give up all but one of the companies that he had created for MONEY rather than be permitted to retain the satisfaction of nurturing those companies into greater profitability. Rearden didn't want the money.
Dagney Taggart gives up all her control of the largest railroad in the country in order to create the John Galt Line. How is that materialistic?
Without intangibles such as glory figured in, it is difficult to explain.
Galt's Gulch exists in the novel as an act of protest against the latter's theft.
That does not change the atheist materialism of the novel's philosophy.