I've often heard the question posed as to why in 1908 Frank Llloyd Wright lost the commission for Villa Turicum to Charles Platt. The answer is simple; Edith Rockefeller McCormick was partial to Italian design.
On the front page of the Villa Turicum website I've quoted Harold McCormick's letter to Charles Platt in 1908: “Mrs. McC inclines to being partial to Italian style. Very glad you’re coming.” Wright had executed a plan for the estate not long after Harold and Edith had acquired the property in 1907, but was dismissed in favor of Platt.
I think it is easy to understand Edith's predilection for Italian design when we remember a few key things that had taken place in the previous years. The movement toward classicism and historicism had been taking shape for over a decade; first with the World's Columbian Exposition (huge public impact) in 1892-93, and second the publication of two important American books: Platt's own 1894 Italian Gardens and Edith Wharton's 1904 Italian Villas and Their Gardens.
Edith's preference certainly was swayed by something, as one architect of a certain style was dropped in favor of another. Although the "American Renaissance" movement (which crystallized at the World's Columbian Exposition) had a tremendous impact on taste, I think Edith's was shaped primarily from the impact of the books. Regardless, when Charles Platt won this rich commission from Frank Lloyd Wright, we could say that it sounded the death knell for (or at least signaled the eclipse of) the Prairie School .
Frank Lloyd Wright, circa 1906
Frank Wright would leave his family in Oak Park and head off to Europe with the wife of a client, leaving the field wide open to Beaux-Arts-trained architects like Platt and the even more prominent (in Lake Forest) Howard Van Doren Shaw.