Why do you love others? Many people today love for very selfish reasons; like: they make me happy; or, they are lovable; or, they are pleasant to be around. Some love because they realize they are obligated to love (remember the second greatest commandment thing?). A few--very few--love because they want to be like God. No, I do not mean they want to be divine, but that they want to love in the same way that God Himself loves. This is the only truly holy kind of love (and it is not impossible for us to accomplish it).
Therefore, the question should now be: why does God love? He certainly does not love because we are lovable (we should know better than to think that!). He also does not love because we make Him happy or are pleasant to be around (sinners who rebel against their Creator are fairly unpleasant). And, it should be perfectly clear that God does not love because He has to do so. So then why does He love us? It is because we are made in His image and as a parent who loves his own flesh and blood, so does God love us (even when we behave like disobedient brats).
Consider loving like that. "That person, who is unattractive and hates my guts, was created in the image of God, and so I love him because I love the God Who created him." That is a selfless love. That is the kind of love that our Lord has toward us; the same love that enabled Him to accept the cross for the benefit of those who were hammering in the nails. Can we love in that way? That is not easy, but since our Blessed Lord went there before us, He understands what it is like. It reminds me of a prayer I came across years ago. It said, "Lord, teach me to love them as You love me". That is true love.