The earliest successful sound for cinema system was the Vitaphone system, which was essentially a gramophone system driven by cogs and cables from the sprocket holes in the film to keep sync! The reason it didn't happen before the late 20's was because there were not powerful enough amplifiers. In the early 1920s power amps could manage about 2 watts, which is less than the power amps in your phone (your home system can probably manage at least 40w and may be able to output well over 100w). So 2w was nowhere near enough to fill a cinema! That's why gramophone players had that huge horn. Today's sound systems in a medium sized cinema are likely to be 30,000w or so!
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