Because Jesus is God's own Son. We are not God with His ability. But Jesus in us shares His love and creativity for how to love.
"And we have such trust through Christ toward God. Not that we are sufficient of ourselves to think of anything as being from ourselves, but our sufficiency is from God," (2 Corinthians 3:4-5)
So, only with God do we have the ability which does what is really good.
Humans in our own sort of loving can tend to be selfish and picking and choosing who is worth loving. We can tend to use people, and be really in love with what we want to use people to get.
Plus, only God's love has almighty power to keep us immune against cruel and ungodly feelings and emotions.
"Let all bitterness, wrath, anger, clamor, and evil speaking be put away from you, with all malice. And be kind to one another, tenderhearted, forgiving one another, even as God in Christ forgave you." (Ephesians 4:31-32)
None of us love like this, without Christ. Plus, only with Jesus can we forgive "even as God".
Oh . . . I think I see how you do not understand what I mean. I do not mean you can not think of someone you love; but I mean the person can not move into your heart and keep making you feel loved, all the time. But yes you can think of him or her, in your heart.
But God lives in our hearts > Romans 5:5 < we do not just think about Him, but He lives in us and personally shares with us. Humans can't stay with us, all the time, and they can't keep us immune against lusts and pride and nasty negative anger and complaining and arguing. Only Jesus in us can do this >
"'Take My yoke upon you and learn from Me, for I am gentle and lowly in heart, and you will find rest for your souls.'" (Matthew 11:29)
"'Peace I leave with you, My peace I give to you; not as the world gives do I give to you. Let not your heart be troubled, neither let it be afraid.'" (John 14:29)
Humans can't keep themselves in peace with almighty immunity against fear and worry. Jesus does.