I've noticed the trend as well, it's said about great white sharks, wolves, mountain lions, grizzlies etc.
However, just because in the past century such attacks were rare doesn't tell us much about today, when in many places the populations of predators are much higher than they've been in living memory. The underlying population of animals is so much larger now (and people so much closer) that I don't think that the twentieth century North American experience with large predators is indicative of current trends.