There are many reasons. For instance, the production of some of them had fallen in the previous few years when the global economy was slack, some were affected by climatic factors, and some were hit by breakdowns at large international plants which reduced their capacity.
各式理由都有，譬如有的是因為前幾年景氣低迷時減產，有的受困於天候因素，有的則是國際大廠臨時發生故障、產能不能完全運轉……。