The people who end up taking these decisions would hardly know the ground reality, passenger profile and so on. They may just look at the system data and hope that some passengers will upgrade to the next higher class . I think there is pressure for increasing revenues and whatever Railway board instructs, zones just seem to follow without even advising or informing the board whether it is right or wrong.
The biggest losers are sleeper class passengers who despite making reservations months in advance end up travelling in coaches which resemble general compartments.