I wouldn't be surprised if the Olaf costume had some restrictions to it that make it difficult to wear, similar to Perry the Platypus. Because of the hard body shell, he has very limited mobility, and his appearances were very tightly controlled. From what I can tell, he did 1 day of M&G in WDW, and showed up at a few Halloween parties at DL, but was restricted to special appearances (non-M&G) beyond that. I wouldn't be surprised if Olaf had a similar construction, which would also make it difficult for him to do much movement and/or interaction; why meet Olaf if he can't actually give you a warm hug?
When Perry was being 'regularly' used there was only one performer who was signed off for the costume, making it even more difficult to have anything resembling a high-capacity meet & greet. Since Olaf is a somewhat late addition, I wouldn't be surprised if they didn't have enough performers and/or costumes to do a proper M&G