The reason they need rationing is because the ship doesn't have infinite reserves.
If some bugger was to stock pile their rations for weeks or months until they could use up the complete ships entire replicator reserve in one fell swoop, screwing over everyone else... Well that would hardly be fair.
The only way to do this with any fairness is to have "no rollover".
If you don't use all of your ration per week, bad fucking luck.
Meanwhile if the ships in the middle of a catastrophe, replicator rationing is going to be wound back to zero and/or ignored.
Of course here's the bonus to such an issue.
Rationing, the amount you get each week, is probably not constant/consistent, but an actual percentage of what ever surplus is allotted for the crew depended on the non fixed actual complete reserve.
Which is odd.
Because the less you use, the more they give everyone, and if you still use even less, then they further give everyone even more.
In New Zealand, a while back, we had a joke political party who wanted to abandon paper currency and replace dollars with kilogram bags of sand. Now you might think that that's insane, but it got worse... On the first day of the month one bag of sand ='s one dollar, but on the 2nd day of the one dollar equals 2bags of sand and so on, until the end of the month when one dollar ='s 30 or 31 bags of sand.
The McGillicutty Serious Party did everything they needed to do to become elected if they did get the votes, but it was truly just an excuse to get violently drunk in a kilt.