The trope did have some basis in RealLife (and in some places of [[SarcasmMode the civilized Western world]] may still have). Not as much in women's supposedly innate (or conditioned by education to brainwashing levels) prudishness, [[RightForTheWrongReasons but as a counter-reaction to the societal pressures around]].
As long as a large percent of men felt due to early-life education and peer pressure their chances of getting social prestige are conditioned by having a female mate ([[TheCasanova or more]]), they would try to accomplish this by [[CasanovaWannabe hitting on any suitable female around]] until they would get lucky, and afterwards would still do it, to preserve their self-enforced image of ladies' men. Even worse in societies where men are pressured into appearing macho to the public and [[UpToEleven worse still]] where men hold most positions of power in state or workplace hierarchies. But this would take for granted any female around, from supermodel to [[BrawnHilda the ugliest troll]], gets her fair share of approaches ...24/7, day by day, for ''decades''. And not only the classic manner of approach, with flowers and love letters, but also the rude forms, including sexual harrassment at workplace and veiled threats if she does not submit. After some time, [[DudeNotFunny it becomes annoying enough]]. So the reasonable women are compelled to do something to get rid of this - either marrying the first suitor on the grounds that a married woman is harder to approach, or becoming prude as a nun[[note]]guys from the [[Literature/TheGame seduction community]] call it "the bitch shield", while claiming at the same time [[AllWomenAreLustful she does it to keep away the unattractive guys]] only[[/note]], for the same reasons. This may also be one of the reasons for which lesbian women play [[ButchLesbian the butch part]] - less for being attractive to other women, but ''to keep guys at bay''.
In addition, the guys who get shot down all the time don't want to think of themselves as losers or unskilled at flirting, as as such they construe those who reject them as prudes or buzzkills. This defence mechanism helps them to keep their ego intact, and also means that they do not have to vary their approach; only their targets.