I wonder if it was to prevent even more chaos around Dinosaur. Imagine how crowded that area would be with a 4+ hr. wait for the ride, Photopass in front of Aladar nearly to Restaurantosaurus, and a Seeker M&G, which you know people would go nuts for.If Dr. Seeker was here, why not have him participate in something last night?
Sometimes I wish Disney would put at least a little effort into the goodbyes for the fans.
That being said, I do wish he had shown up at the end. Maybe greeting the last people to get off the ride or walking the queue after the line cut off.