Victorian morality and prudishness came in as a reaction to the C18th libertines, I think.
That's the usual story, but I'm dubious, because it places the elite in a cultural bubble. If you look at contemporary literature, the primary target of moralising rants aren't libertines or even aristocrats, but the urban poor, who are regarded as lacking either the moderating constraints of rural society or the natural self-discipline of the middle class. Victorian moralism seems to me a reaction to the confrontation of the industrial bourgeoisie with the "dangerous classes" of industrial society, rather than simply a generational trend within the elite.
This social dimension of Victorian morality really must be stressed, because it wasn't simply neo-Puritanism, it was very explicitly a concern for
public morals. This is a change from the eighteenth century, because it expressed an experience of "public life" that hadn't existed before industrialism, when life was far more localised and communities were understood to be generally self-administering so far as issues of morality were concerned. (Significantly, earlier complaints were usually directed against vagrants, such as itinerant workers and Roma, who were threatening precisely because they existed outside of the community.) Victorian morality required the creation, or perhaps we should say discovery, of a mass society, and was a reaction to the threat of disorder (and even revolt; the two were not clearly distinguished in the bourgeois Victorian mind) implicit within that society.
And in that sense, Victorian morality is alive and well, among both liberals and conservatives, who compete to assert the means by which the poor shall be rescued from themselves. If there's a difference, it's that Victorians at least believe the poor could be elevated to a state of self-discipline, however many generations it may take, while it's now accepted as common sense that the poor are eternally and irreparably incapable of self-government, and the debate is simply as to the proper ratio of stick:carrot. It's largely dropped the Puritan edge, but that's because it was never really needed in the first place, but was rather a cultural quirk of Anglo-American Protestant culture, and nowadays public moralism and consumerist hedonism can sit quite happily side by side.
"Oh, there you go, bringing class into it again." "But that's what it's all about!"