I work at a major pattern company. There is no reason to update sizes, as the pattern sizes are the "true" sizes. The ready to wear industry keeps changing their sizes, so that you will still buy their clothes, and their sizing is referred to as "vanity sizing",meaning, the same size keeps getting smaller numbers on it, for the vanity of the wearer.
Also, pattern companies are regulated. The major ones must keep the same sizing standards. If we werent, think of the confusion, trying to choose what size pattern to make.