Despite being part of the same Continental West Germanic dialect continuum as the various German dialects and regions that would eventually be subsumed into a German national identity and standard language, the Low Franconian speakers of the Low Countries instead built their own identity and standard language that continues this day as the Netherlands. Why is this?
Because politics. The lowlands were part of the Holy Roman Empire from around 870s till the 1500s. However in the 16th century the HRE and the kingdom of Spain and Southern Italy all fell into the hands of one man, Charles V. Charles eventually abdicated and divided his lands between his son Philip 2 and his brother. The brother became HR-emperor, but his son Philip became king of Spain, Napels and the lowlands. This seperated the lowlands from the HRE. Eventually, the mostly protestant Dutch revolted against their devout Catholic King. No longer being part of the HRE and revolting against their king made the Dutch Republic a de facto independent state. This independence further seperated the Dutch from the rest of the continental Germans politically, historically and culturally. This also gave rise to the split between Dutch and Flemish Identities, as Flemish lands stayed in the Hands of Catholic Spain, and later Catholic Austria, while the Netherlands went on being a Calvinist Republic.
When the german empire was being re-created with the Prussian King as Emperor, the Netherlands had been seperated culturally and politically from the rest of the Germanic States for over 300 years. In this time the Dutch and Flemish created distinct national indentities from other continental Germanics.
I am not sure I am reading this right. Isn't Dutch a Franconian language? It's more related to Frankish than Low German.