Wilde certainly did not invent English facetiousness, but permanently re-established its fashionability
It is found in medicine, law, and all the professions. And it has spread to include more people all the time.
Facetiousness is high status, and earnestness a sign of unintelligence and/or dangerous fanaticism.
But facetiousness is something that precludes genuine attainment - and for the best artists, musicians, writers, creative scientists etc, facetiousness was a pose that needed to be dropped when serious work was afoot; only to be resumed when 'normal life' was resumed.
So, facetiousness made the intellectual class radically and ineradicably two-faced, and unintegrated as personalities. It was what made many of the great geniuses of England intolerable as people to the geniuses of other nations (e.g. cultural Germans such as Wittgenstein, Karl Popper). And intolerable to working class geniuses (such as DH Lawrence and Colin Wilson.)
Indeed, probably the reason why I have always noticed and disliked this aspect of Englishness is that I have the hereditary earnestness of someone from a working class background.
And this lack of integration, further, was a weakness at the heart of English life since the terrible religious civil wars of the seventeenth century.
My guess is that this facetiousness emerged in the period of the Restoration (King Charles II - for instance the 'Restoration comedies') and became dominant in the middle 1700s (the author Laurence Sterne was an exemplar).
My interpretation is that it was related to the rise of the Romantic impulse, which came first among the upper classes - then worked down. Facetiousness is a denial of Romanticism, a keeping-in-place of Imagination, so that imagination would not disturb the growing materialism; the growing pragmatism, bureaucratization, scientism which underlay Britain's rise as a world power and the first industrial nation...
The positive excuse for facetiousness was probably to avoid the religious wars. The rationale was that if religion was made a superficial matter, then it would not motivate people enough to fight about it. This was true, people were thus demotivated; and it was effective in that specific goal.
(The lower classes found this intolerable, and there were several nonconformist (i.e. not state religion) revivals among them from the late 1700s onward. But then they, too, were incrementally affected by facetiousness - perhaps mainly via the mass media and the sexual revolution.)
But the demotivation did not stop there - far from it - it became all-pervading (esepcially after 1945, and more so fater 1967).
Because we have a national ethos of facetiousness, the English (and British more generally) are probably among the most demotivated people in world history. And therefore among the least able to learn from spiritual experience.