1) 1912-1930 would probably be best described as a golden age of Slapstick, rather than of comedy in general. This is the era, and the Vaudeville years that preceded it, when the various bits and gags were developed and shaped into their sharpest and most memorable forms. While there are still plenty of examples of slapstick and physical comedy in modern film in many ways they will be a retread or tribute to a gag from the "golden age"
2) The silent era of film couldn't rely on wordplay or clever dialog to really land a good joke, but the purely visual medium made physical humor and clowning a natural element. There are still plenty of good sight gags and physical comedy to be had in modern television and film.
3) Compilations and documentaries have a great ability to combine a large amount of source material spanning many years and compress that information into a digestible volume. While good for hitting the high points, there are inevitably smaller performers and less known films that could get overlooked.