Answer:
An author might use ethos because it will help to convince the readers about his credibility and like that they will believe what he/she says.
Step-by-step explanation:
Ethos refers to an argument that tries to persuade the reader about the credibility of the author. He/she will use ethos to convince the reader to believe on his/her ideas.
Also, the author would try to generate trust and similarity as an audience will be persuaded easily if they trust you, and if they can relate to you, they would be more willing to listen to what you have to say.