I've been searching for a deeper back story on the origins of modern witchcraft, and this search appears to end with Margret Murray and theorists of the 19th century. I can understand debunking the notion that the witch trials were attempting to squelch an anti-christian occult presence. I can even understand that most pre-christian spirituality was either assimilated, acculturated or violently stamped out so that little evidence is left aside from caricatures passed down from generations. Now granted I have only just begun this search and have not had a chance to read the arguments debunking the existence of continuity between ancient and modern witchcraft, but given that anti-witchcraft laws were only lifted recently (some still exist), coupled with no small amount of Christocentrism, is there really nothing linking revivalist movements to something genuine?
Are you asking whether witchcraft exists as a supernatural thing (in which case we might direct you to a theology sub); or whether there is continuity in what one might call "folk practices" of witchcraft from the pre-Christian era to the modern era?
Why do you assume there would be cultural bias, in the late 20th and early 21st centuries, against uncovering a continuity of witchcraft or magic in Europe?
It might have been true, once upon a time. History was traditionally the story of popes and princes, the royal chesspieces of the past, building the foundations of the modern world. Especially in Europe well into the twentieth century, where the Middle Ages play such a strong role in so many national mythologies, the effort to make the era into the cradle of modernity did, in fact, prevent historians from even being able to see layers and layers of the Middle Ages. For example, the existence of women. I don't mean at all to suggest this was malicious or conspiratorial. Women's lives, the religious ("superstitious", at the time) ideas of non-priests/non-theologians, whatever it was that those the Church deemed "heretics" believed--these things weren't even seen, because studying them would have no point.
In the second half of the twentieth century, that changed in a BIG way. "History from below" in various forms shifted the primary thrust of medieval history to social and cultural approaches. Combined with a sort of de-nationalization (or at least, the attempt thereof) of history that gradually gained steam after WWII--and, not at all coincidentally, the decreasing dominance of Christian faith in North Atlantic academia--historians fell head-over-heels into the worlds of medieval peasants, townspeople, women, heretics, theologians translating books of sorcery on the side. Medieval people who placed themselves in (what we perceived as) opposition to the Church became the heroes of scholarship, not the villains. Indeed, to the extent this stance was very frequently overblown in scholarship.
Even the people continuing to chug away at political history or interested in rebuilding a cohesive narrative of the era today have to account for this tsunami of the "popular" Middle Ages that is still such a force in scholarship. Medieval English literature cannot get enough of the Lollards (heretical movement), to the extent that there is now an entire subfield devoted to pointing out that there were other things going on in English writing in the 14/15th century, really, they promise they were.
The point is, medieval scholars would like nothing more than to uncover the reality of witchcraft in medieval Europe, IF there were actually a historical practice of witchcraft. Whether there's still a sheen of romanticized "let's be subversive and undermine the Church" or just the burning desire to understand a time period that seems so normal in one moment and without warning slips into a complete and total mindwarp (seriously, the Middle Ages are awesome), we want to understand the era! How would the deliberate, calculated, coordinated strategy to cover up magic help us understand what was really going on?
If, on the other hand, you just mean "couldn't the witches have hidden everything," that's more a question for r/conspiracy.
Incidentally, England un-outlawed witchcraft in 1735. Instead, they made it a crime to fake supernatural powers, especially for profit. (And indeed, that was/is the condition under which "witchcraft" stayed illegal so long--its use to turn a profit, because legal authorities believed it was all faked so any profit was fraudulent gain). That would seem like a prime opportunity for actual witches to step up and say, "See, but our powers are legit."
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Sources: Medievalists love to talk about medievalists. A good intro to the shift in medieval studies I sketched out here is Paul Freedman and Gabrielle Spiegel, “Medievalisms Old and New: The Rediscovery of Alterity in North American Medieval Studies” (AHR 103, 1998); also see John Van Engen, "The Christian Middle Ages as an Historiographical Problem" (AHR 91, 1986)
nb: My concern here is strictly witchcraft/magic in Europe and medieval European historiography, as that's how I interpreted the scope of OP's question.