The noble's reason for joining in such droves was quite natural if one thought about the terms of the proposal a bit.
Alexander by design had made the proposal such that it made more sense to join him and receive the economic benefits rather than choose to stay isolated and all alone, with all the downsides to leaving Amenheraft and none of the upsides of joining Alexander.
Hence other than the most staunch supporter of Amenheraft, Lord Yuusuq, everyone flipped.
"Hahaha, it is great to see you make the right choice. You won't regret it." Alexander patted the arms of each man as he greeted them, and then decided to schedule the coronation at the Temple of Ramuh in a month.
The reason for requiring this large amount of time was because of a few reasons.