The answer can be found from evolutionary psychologyevolutionary psychology. We are wired to feel fear when we encounter stimulus that look like spiders and snakes.
Evolutionary psychologists argue that much of human behavior is the
output of psychological adaptations that evolved to solve recurrent
problems in human ancestral environments
Spiders and snakes were major threads in the early years of the evolutionary history of humans. Human ancestors that were more afraid of spiders/snakes had an evolutionary advantage over those who did not, because they were more cautious and survived more years.
people nonetheless learn to fear spiders and snakes about as easily as they do a pointed gun, and more easily than an unpointed gun, rabbits or flowers. A potential explanation is that spiders and snakes were a threat to human ancestors throughout the Pleistocene, whereas guns (and rabbits and flowers) were not. There is thus a mismatch between humans' evolved fear-learning psychology and the modern environment.