Why do animals attack and eat people

Because people are animals and that is how the balance of nature works. Animals eat other animals to survive. They avoid the creatures that are likely to eat them and attack the ones that they can kill without being killed. I don't think there is much of a threat to people from snakes. Few snakes are big enough to eat humans. But, they can kill humans, if they are a threat, and we often are. It's defensive rather than aggressive.

You are correct that if people did not have this level of intelligence, there would be few humans around. The odds that a person can live from birth to adult is very high, approaching 100%. For most animals in the wild, the odds of being eaten in the wild before they grow to adult is usually well over 50%.

Because they are carnivorous and that's how they survive - - they kill to eat and defend when threatened. Most animals also have predators that they are fearful of and use their instinct to survive or be killed themselves. Not pretty sometimes, but it's survival of the fittest.