The answer is that he had to be the closest eligible relative, as well as needing to be willing and able. Hey! You’ve made it to the very last question! Don’t be a dork and blow it all now, please.
Now, mankind had lost everything to sin. We needed someone to redeem us. Someone became a human being so that He would be our near kinsman. He was very willing, and because He was sinless, He was the only one able to redeem us. Who was and is THE Kinsman-Redeemer?