Why does codecademy Http Request lesson force you to use arrow functions?

Hello! I just finished Intermediate JavaScript. It seems like http requests are the last lessons in there, but theres something that is bothering me…

If i were to choose a function, i would choose this:

const JS = function() {

}

because i like the format better.

But when i did the http request lesson, i came to this, for an example:

Set the xhr.onreadystatechange event handler equal to an anonymous arrow function. Leave the function empty.

And i had to do that in whole http request lesson, even http request 2.

Why did i have to use arrow functions in just these lessons but not on others?