A horse costs way less than a scroll of Teleport, or seven Fly. Like how it's cheaper to drive than take a plane. You also don't take a plane when an hour long drive will do, and you don't cast Teleport to go from your room at the inn to the nearby village to clear out some goblins.
Towns can hire wizards to make teleportation circles to make quick cheap travel to specific places. No one more than an hour's ride from a capital would use any other way of getting there