In A Discovery of Witches, there's a large contrast between the magic world and the normal world. This is something that has a large effect on the main character, Diana. She talks about how her mother looked like anyone else's by day. However:

In the privacy of our home, with the curtains drawn and the door locked, my mother became someone else. Her movements were confident and sure, not rushed and hectic. Sometimes she even seemed to float. As she went around the house, singing and picking up stuffed animals and books, her face slowly transformed into something otherworldly and beautiful. When my mother was lit up with magic, you couldn’t tear your eyes away from her.

This lays the basis for Diana's rejection of magic—which doesn't last long once she finds a book that draws her back to the world and forces her to rethink her past. The magical world exists but is largely unseen by humans. That's the world Diana turned her back on to be an academic.

Diana discusses the change in the world with vampires. They talk about how humans slowly snuffed out the idea of magic as something real. Deborah Harkness writes:

Common sense told me to remain silent, but the knotted threads of my own secrets began to loosen. "I wanted to know how humans came up with a view of the world that had so little magic in it," I added abruptly. "I needed to understand how they convinced themselves that magic wasn’t important."

The vampire's cool gray eyes lifted to mine. "Have you found out?"

"Yes and no." I hesitated. "I saw the logic that they used, and the death of a thousand cuts as experimental scientists slowly chipped away at the belief that the world was an inexplicably powerful, magical place. Ultimately they failed, though. The magic never really went away. It waited, quietly, for people to return to it when they found the science wanting."

This might be why many of the supernatural creatures in the novel seem to be drawn to academics. It's a place where creatures can continue to use at least one type of magic. Also, it helps improve the world which certain vampires have attempted to do throughout the centuries.

Since so many of the creatures in the novel live long lives, there are also a variety of different customs and attitudes in the novel that aren't present in a modern-day setting. For example, Diana thinks:

The past seemed gray and cold without Matthew. And the future promised to be much more interesting with him in it. No matter how brief our courtship, I certainly felt bound to him. And, given vampires' pack behavior, it wasn't going to be possible to swap obedience for something more progressive, whether he called me "wife" or not.

History is important in the novel. Diana and Matthew both have family involved. The lines of their families, as well as their supernatural types, govern the novel because they create a set of rules that establish the natural order of the world. Of course, the possibility of a witch giving birth to a daemon baby calls these rules into question—but the combination of history and science helps to explain exactly what is happening with the cast of characters.