let myname ={
    firstname: "Fname",
    lastname: "Lname"
}

let printName = function () {
    console.log(this.firstname + " " + this.lastname);
}

let printMyName = printName.bind(myname);
printMyName();

This code gives output 'Fname Lname'

let myname ={
    firstname: "Fname",
    lastname: "Lname"
}

let printName = () => {
    console.log(this.firstname + " " + this.lastname);
}

let printMyName = printName.bind(myname);
printMyName();

This code gives undefined for both the variables.

Why does this happen?