There are a very large number of possibilities that might be improbable for anyone to guess. If Q has 'control' in order to make predictions, couldn't he be controlling individuals in a way that a mechanism we can't predict will be used? Even for a dedicated anon, it might simply be very hard to predict. This is not the same thing as them not having enough 'control' for a very wide range of effective and independent possibilities to be at their disposal.