Why exactly did Dev fail to recognize the Sanyasi as being Sai Baba in disguise?

Dev failed to recognize the Sanyasi as Sai Baba for a specific reason that created a "veil of Maya." According to Chapter 40, this particular Sanyasi had visited Dev before the Udyapan invitation was even extended to Baba. That initial visit was for the purpose of collecting funds for cow protection. Because Dev had this prior, mundane interaction with the Sanyasi, when the same person appeared for the meal, it did not occur to him that this could be Sai Baba. Dev later lamented that his vision was confused by this sequence of events, admitting that if the Sanyasi had appeared only after the invitation was sent to Shirdi, he might not have been so deluded.