Here's why:
* First person uses "I" or "we" (e.g., "I am saying this").
* Second person uses "you" (e.g., "You are saying that").
* Third person uses "he," "she," "it," or "they" (e.g., "They are saying it's true").
In the phrase "saying," the subject is unspecified. It refers to an action that someone (or something) is doing, without specifying who that someone is.