But the earliest clear indications of believers treating Jesus as sharing in divine honor and as rightful co-recipient of worship are found in our earliest texts, dated ca. 50-60 CE. And, indeed, in these texts, this treatment of Jesus is taken for granted and as uncontroversial among believers, which suggests that it was by the time of these letters already traditional. As Martin Hengel once observed, in historical terms, more happened christologically within those first few years than in the ensuing 800 years of theological development.
My view point: This high Christology started around 53-54 through the effort of Paul & Apollos of Alexandria.
Motives:
A) Explain why a Christ would be crucified (a thorny issue) and what consequence that would have for the ones "in Christ". That is salvation at a time when it was expected a new Divine order was coming soon (with God's wrath to be delivered on the non-elects).
B) The Gentiles converts did not want to be second to Jews (or for the males to circumcise) and not sure if they were eligible. They needed their own stand alone religion, based on a heavenly Savior (with human experience), with all kind of reassurances. Consequently, Jesus was elevated as a god, and one with the power to collect (& later even resurrect) elects for the Kingdom of God. (however, the Jewish origin of Jesus and of the ensuing sect could not be denied and remained at the core, despite many later attempts to get rid of that).
C) Competition in 50-60 was fierce, almost like war among different apostles, forcing some of them to be innovative, in order to find on the fly (and forcefully preach) new christological claims attractive (even if they were considered controversial by others) to Gentiles.
Note: most of these Christological innovations were made away from Jerusalem and even away from the then center of Jewish Christianity, Antioch. That was done in areas around the Aegean sea, where, through the efforts of Paul, Christianity had just been introduced, in places where Jews were not very numerous (more so for Philippi and Galatia).
All of that would explain the Christological advances on a relative short time, even if many of these claims were not fully accepted right away.
Cordially, Bernard