I wonder what is the real reason
Because how they defined witchcraft is often times harming another through magick, working with evil spirits, magick for evil things, and so on.
… and edge lording is fun?
If you go back and read history, witches were healers, brewers, midwives and herbalists. The edgy part is a new invention of the church during it’s political attack on private industry and personal empowerment and knowledge basically… it’s medieval propaganda, and can be safely ignored. 
If you want to explore the “darker” aspects of human nature that’s available too, but it’s not a must.
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It somewhat depends. Talismanic magick was a large thing in those days, as well as magick through herbs and stones.
Certainly the witchcraft thing was a means to oppress women and groups the Christian church didn’t like. But what they considered magick was a bit more complicated. There are many authors who wrote on Magick during the Renaissance, such as Agrippa, Marsilio Ficino, John Heydon and were never persecuted for it (Agrippa is debated). Even the Medieval Christian Saint and one of the 36 Doctors of the Church, Albertus Magnus, approves of Talismanic Magick.
However, they removed the instructions on creating baneful talismans that were present in their sources (Agrippa excluded), as this would raise suspicion from the Church that evil spirits could be involved.
Now, as for what they considered witches, William Lilly says of the 12th House of Heaven “It hath signification of private Enemies, of Witches … Sorrow, Tribulation, Imprisonment, all manner of affliction, self-undoing, &c. And of such men as maliciously undermine their neighbours, or in-forme secretly against them” (Christian Astrology, 1st Ed, Book I, Page 56)
So, we see the association of Witches with curses and afflictions. The 12th House was used in divinatory questions regarding curses. So a witch was regarded as different from simply a magick practitioner (and the practice of benefic magick is attributed to the 9th House).