Why did Low German decline after the Hanseatic League declined?

The decline of Low German as a written and administrative language was closely tied to the waning influence of the Hanseatic League. During the league's period of prosperity, a standard Low German written language had begun to develop, supported by the commercial dominance of northern German towns.12

However, as the Hanseatic League declined between the 15th and 17th centuries due to the loss of its trade monopolies, shifting European trade routes, and internal political fragmentation, the impetus for a unified Low German standard diminished. Simultaneously, the rise of East Middle German dialects—which were used in the chancelleries of Saxony and famously employed by Martin Luther for his Bible translation—provided a more prestigious and widely accepted basis for a standard language.321

Because Low German never reached full maturity as a standardized literary or administrative language, it was eventually superseded by this emerging High German standard, which became the official language of administration, literature, and education even within the northern lowlands. Today, while various Low German dialects persist in spoken form, no single literary standard exists.12