So, there was a market for prophetic texts of unknown provenance in Rome at this time, and generally the people who produced such works were presumably just using it as a way to make a living. It was similar to how Indian gurus work today, doing things like magic tricks to fool people who donating money to them. It's not for some grand plan, its just their means of making a living. I suspect strongly that's why the Gospels of Matthew and John were written. Luke appears to have been written by one of the scholars who was commissioned by a wealthy patron to investigate the Gospel stories, thus he produced for him what he thought was a revised and corrected account, having worked from Mark, Matthew and the letters of Paul.