Twilight question; if humans are just getting the technology to kill vamps, why do the vamps hide from us?

As stated many times, humans are completely defensless agains the vampires; we have no means to kill them, although as stated in BD, technology is starting to become a threat. So exactly why do the evil vampires (such as the Volturi) who like humans only as food hide their existance? Isn't it similar to a cat hiding from a mouse?