Mostly because vampires seemed like the most logical ones to spread out, and I... admittedly haven't put much thought into the Western monsters yet. ^^; Unless you count demons but those skirt the line of being overpowered in terms of this setting.

The very first character I ever made for this setting was a vampire, which is why they're the only representatives as far as Western monsters go. Everything else as kind of just come up as I've needed it for something. ^^;