Simply because..

God’s love is incomprehensible and unchangeable. For it was not after we were reconciled to him through the blood of his Son that he began to love us. Rather, he has loved us before the world was created, that we also might be his sons along with his only-begotten Son—before we became anything at all. -Augustine

"But God demonstrates his own love for us in this: While we were still sinners, Christ died for us." -Romans 5:8

Somethings just don't make human sense. Such amazing love. Ever pondered why?:

"As the heavens are higher than the earth, so are my ways higher than your ways and my thoughts than your thoughts." -Isaiah 55:9

"I will have mercy on whom I will have mercy, and I will have compassion on whom I will have compassion" -Romans 9:15

Sometimes the answer is 'simply because'. And that makes it all the more glorious.