What's the purpose of the underscore if you can just different words for getting and setting?

class Pet {
    constructor(animal, age, breed, sound) {
        this.animal = animal;
        this.age = age;
        this.breed = breed;
        this.sound = sound;
    }

    set setOwner(owner) {
        this.owner = owner;
        console.log(`setter method called`);
    }

    speak() {
        console.log(this.sound);
    }
}

const casper = new Pet('cat', 10, 'ABYSSINIAN', "meowmeowmeow");
const ernie = new Pet('dog', 10, 'pug', "Woof!");

ernie.setOwner = 'Ashley';
console.log(ernie);
console.log(ernie.owner);

treehouse:~/workspace$ node pet.js                                                                                        
setter method called                                                                                                      
Pet {                                                                                                                     
  animal: 'dog',                                                                                                          
  age: 10,                                                                                                                
  breed: 'pug',                                                                                                           
  sound: 'Woof!',                                                                                                         
  owner: 'Ashley' }                                                                                                       
Ashley