It’s because Jesus knows us completely that he knows how completely we need to be saved.
And that’s how he reveals the gracious magnitude of God’s love.
From Chad Bird:

Jesus knows good and well that there’s nothing inside us worth believing in. In fact, everything inside us looks absolutely untrustworthy. If anything, when the Lord peers into our hearts, he should hightail it for the hills, getting as far away from us as he can. But he’s not that kind of God. He loves before he looks. And even after he looks, he still loves. Because his love has nothing to do with us. It is not sparked by our goodness or sustained by our obedience. God is love. It’s who he is and what he does. While we were still powerless, he was powerful to save. While we were still sinners, he was still the sinless, gracious, saving God he’s always been.

Chad Bird, Upside-Down Spirituality: The Nine Essential Failures Of A Faithful Life, Baker, 2019, pg 44.