The earliest title with this format that I know of is "Is Sex Necessary? Or, Why You Feel the Way You Do" by James Thurber and EB White from 1929. But, that book was a parody so presumably copied the form of its title from contemporary books.
The most famous book title I know with that format is Frankenstein, or The Modern Prometheus. It's so old a style that I find it funmy that it could be seen as a fad.
True, but I was matching on "or, why" not just "or".
According to wikipedia even shakespeare parodied the style of subtitles in "Twelfth Night, or What You Will", so again much older than 1929.