Because most of these imported spices won't grow in Europe. Black pepper, nutmeg, or allspice must live in true tropics, preferably not far off the equator. Take cinnamon, a tree with no tolerance for cold, whose bark has to be peeled off and dried to produce the spice. Even in the tropics, you can't grow it at higher altitudes.

You might manage to grow a cinnamon sapling in a greenhouse, but you couldn't raise them on a commercial scale.