What prevented Aristotle from discovering atmospheric pressure 2000 years earlier than Torricelli?

Delusion. Aristotle believed that nowhere in the world there can be empty space and he explained all the known observations that are associated with the action of atmospheric pressure by the fact that nature abhors a vacuum.

Remember: The process of learning a person lasts a lifetime. The value of the same knowledge for different people may be different, it is determined by their individual characteristics and needs. Therefore, knowledge is always needed at any age and position.