Witches, in essence, are people who can use mana without the involvement of God or Goddess. They were being hunted since ancient times because of the same reason as people believed they were worshipers of the Devil.
The Gods and the Saints knew the truth that there was nothing like that, but still hid from these people because they were looked at as a threat to their position. After all, their power would decrease if others started doubting their gods in any form.
But things were not as simple as that. For people who needed to believe in a God to get their power, witches could directly tap into the power of nature. The only limit is their own understanding of the nature they were affiliated with.
Hence, between surviving and thriving, the thriving part became more prominent over the decades.