Here's an interesting perspective on the situation. I was discussing this with a friend who works on case processing, though not specifically for immigration. He mentioned that the process tends to be smoother when they handle cases in batches.
If you request your case notes, you might notice that your citizenship has already been granted once your LPP is completed. You may also find that you were assigned to a specific group mentioned in the notes.
Now, this is just pure speculation, with the latest news that IRCC is moving towards a 'priority cohorts' system, makes me think that some offices might already be using a mix of cohort-based batch processing and single FIFO (First In, First Out) processing.
If you're processed as a single case in FIFO, you're probably assigned an oath date as soon as your LPP is done, and they likely fit you into the first available oath date. However, it's possible that some offices also use the cohort system, where they wait for the entire cohort's LPPs to finish. Once all the processing for that cohort is complete, they probably assign the entire group a single oath date together.
So essentially, if you're in a cohort, you have to wait for everyone's LPPs to finish within your group, then wait for an opening on the oath calendar for your group, and only then will you get assigned an oath date. This could explain why some people get their oath date immediately, while others, like many of us, seem to have to wait somewhat arbitrarily. It might also clarify why some offices, particularly the less busy ones, give out oath dates quickly, while busier ones like the SCR office tend to assign oath dates much later. It probably also explains why the same office sometimes hands out oath dates earlier or later in the year to certain people. Because it all depends on how busy the office was, and if you were assigned to a cohort or the FIFO system, the proportion of which I think changes depending on seasonality and incoming cases to the office.
Again pure speculation, but it does explain some of the observations, and if its true, this basically means that once your LPP is complete, just sit back and relax. You probably can't control anything at this point, you just have to wait till a spot in the oath calendar opens up for you.
