My guess is, once your processing time passes the one-year mark, you are no longer in the pool of people who are processed 'within 1 year or less', and in order for IRCC to keep reporting they can finish 80% of cases within that time frame, they need to focus their resources on people who haven't reach that 12-month mark yet. For us who have waited for more than a year, we no longer matter to them, since no matter when they finish our cases, we will always be in the 20% that will take more than a year