Chaos theory or industrial espionage. I do not know what the cause, but the truth is that I have been watching for years many cases of artistic productions (call it so), apparently about the same, which occur simultaneously. I think some of them are the result of an esoteric phenomenon I call Concurrent Creativity.
Perhaps the most striking cases are those of the films. Do you remember the launch about the same year of two films about illusionists? Do you remember two animated films featuring a fish? Or an ant? The same thing happens with books. Perhaps you can recall some examples; it would be nice to have a list.