There are actually a number of different theological theories regarding Christology. The question you're asking assumes the standard "Infralapsarian" line of thinking. This form of Christology suggests that the incarnation of Jesus is contingent on human sin. However, another major school of Christology is Supralapsarian Christology, which posits that Incarnation is not solely motivated by sin, and that God may have other reasons to become human. The biblical account suggests that Jesus is the particular way God chose to deal with "the sin problem," though it may not have been the end goal of the Incarnation. This gets into different theories of Creation and Eschatological Consummation. Perhaps God is interested in relationship with creation that the Incarnation accomplishes more than just dealing with sin.
See:
"Supra/Infralapsarianism" by Edwin Chr. van Driel in, "T&T Clark Companion to Atonement," edited by Adam J. Johnson. Bloomsbury T&T Clark, 2017. Can *maybe* check it out here or here.
Also if you can drop the $:
"Incarnation Anyway" by: Edwin Chr. van Driel.