The Dutch connection?

Why is there such a preponderance of Dutch people in this novel? Three out of the novel's eight main characters are Dutch, or at least have Dutch names: Lucy Westenra (the suffix "-a" being specifically Frisian), Mina Harker nee Murray ("Mina" being short for "Wilhelmina", a Dutch name if ever there was one) and of course Professor Abraham van Helsing from Amsterdam. If this novel were real life, you'd just call it a coincidence. But it isn't real life, thank Buddha - it's a novel, and when authors make choices they have reasons for doing it. What was Stoker's?