Why don't people believe that some animals want to eat us?

animals don't care about us they will eat us those people just try to protect animals and they wont admit when they are wrong

To think that all animals honor us is as unrealistic as to think all animals want to attack us. See that spider? It might jump up and bite you!
I don't think many animals have Human as part of their ordinary diet; that doesn't mean they would never eat one. Of course herbivores don't eat humans.
It's a good idea to have some idea of the animal's agenda in life, yes. It's true that many attacks on humans are cases of mistaken identity, or were provoked (maybe unintentionally) by the human. For instance, a hunter in full camouflage, lying prone on the forest floor, blowing a turkey call, gets jumped by a mountain lion: that was mistaken identity! Imagine the cat's surprise when the turkey starts yelling and hitting with his elbows! Bet it learned a lesson.
Then again, if the human blunders into the vicinity of the helpless cubs, the human might get an unpleasant surprise. This was the human's mistake! A quick retreat would be in order.
But frankly, a carnivorous animal has no more moral compunction about eating a human than we do about eating another animal. Why should they?

Certain animals do indeed prey on humans. The most famous case in the tigers of India. However, the animals that are not reluctant to kill and eat a human are all terrestrial carnivores that evolved with humans.

Marine predators do not have a clue about humans. We humans have only been sharing their habitat for about 20000 years. So great white sharks have not evolved with humans. They simply don't have a clue we are a potential meal.