Confusing use of 減る Maruko is complaining that mum is buying seaweed as a new year's present. Mum replies: > **** > There are plenty of opportunities to eat seaweed, and because they **immediately decrease** , when one receives it they are grateful. Why do the opportunities to eat seaweed decrease? Is there some cultural knowledge I'm missing or is my translation wrong?

What decreases is the stock on hand. In other words, Maruko's mother is saying that, since people eat nori on so many occasions, **one's supply** runs out very quickly, and so one is happy to receive it. Think of a big pool of available nori that gets drained as it gets used.