It's hard to know from the outside how these things work. I work in a different ministry, and step one with a file is basically data entry, followed by contacting the client. If the file is complex, it might take a lot longer at later stages, but not at the initial stage. I would think the immigration agents processing citizenship files are probably assigned batches of files, and if they have an inventory of complex files they are already working on, they might not get to the new ones for a few weeks. Or they might be on vacation, or sick leave, or get promoted, or transferred to fix Phoenix... you never know!