To understand why, we need to look back at 3D's history. This stretches back further than you might expect - right into the earliest days of silent cinema. The first 3D processes emerged at the very beginning of the 20th Century, and the earliest 3D presentations appeared as far back as 1922. However, it was in the 1950s that 3D cinema first hit the big time. Then, as now, there was a feeling that cinema was in a crisis. Attendances were down, audiences were shrinking, and Hollywood needed something to drag audiences away from their new-fangled TV sets and back into the cinema. This was a golden age of technological development for Hollywood - the time of VistaVision, Cinemascope and the 70mm epic - and for a while it looked like 3D might just eclipse them all.
Strangely enough, the film that bought 3D into the mainstream wasn't a big budget studio picture but a small, bargain-basement production. Bwana Devil (1952), a tale of man-eating lions on the East-African railroads, was shot in stereoscopic 3D using a process called Natural Motion. It wasn't exactly sophisticated. Two 35mm cameras were stuck together and geared to run in sync. Cinemas showed the two resulting films through two synchronized projectors, each with a polarising lens, on a specially coated silver screen. When viewed using glasses with polarised lenses, the brain was fooled into combining the two images into one image with a perceptible sense of depth.
The technique was crude, the film laughable, and yet Bwana Devil was a hit. Despite its lack of star power - a pre-Untouchables Robert Stack and a post-Sherlock Holmes Nigel Bruce had the leading roles - it broke box office records in the LA and Chicago cinemas where it was shown. Hollywood noticed and liked what it saw, and so the 3D boom of the 1950s began. The films were still shot and shown using variations on polarisation, but the production values and techniques were much improved. It's a wave remembered best for sci-fi and horror genre pieces like 1953's Vincent Price fright-fest, House of Wax, or It Came from Outer Space, Creature from the Black Lagoon and Cat Women on the Moon. Yet 3D also attracted high-calibre mainstream talent, including Hitchcock (Dial M for Murder) and John Wayne (Hondo), and even made it to such popular genres as the musical (Kiss me Kate).
Unfortunately, in its earliest incarnation 3D had serious issues. Shooting and distributing 3D film was expensive, and projecting it difficult. To show a 3D film correctly, the two projectors had to be run in perfect sync and with optimal focussing, or the experience became uncomfortable very quickly. As a result, the studios retreated from 3D in favour of the easier to handle widescreen and 70mm formats, and 3D began to be associated with gimmick-laden, B-grade genre efforts. Focus shifted to the cheaper Anaglyphic system - the familiar 3D format where a single image with red and blue layers could be decoded by matching lenses for each eye. Slowly, 3D became the province of cheap exploitation and even soft-porn rather than major studio productions. It seemed that 3D wasn't ready for the mainstream, and the mainstream wasn't ready for 3D.