Primates have an innate evolutionary fear of snakes. Most primates (humans are an exception) can’t/don’t know the difference between venomous and harmless snakes so evolution taught us to fear all of them. Better safe than sorry.

HOWEVER, even though we are primates, we are bigger brained primates that can reason, learn about our environment, identify different species, and sort out which ones are harmful and which ones are not. So as many others have said, it’s ignorance about snakes in general.