Every year they run a number of antiquated and tetchy computer programs to determine how many pilots each fleet and seat needs, and process expected retirements, and internal bids for fleet and seat moves. Every time they think they have a solution, somebody changes the flying plan for next year. This requires a complete re-run, re-plan &c. Once the plan is complete, it needs approval. Finance may elect to trim the plan again, requiring another cycle or two of the above.
Only once this merry go round has ended do they have a plan for what is required, and the pilots get annual bid results. They also know how many new recruits they need, and in what fleets. They may have enough of an inkling before this is all over to make some offers for Jan/Feb but the vast majority of offers are likely to be held back until this process is complete. Last year it was late November...