Agreed. IOTL, rapid industrialization focused almost exclusively on the Ruhr region, the Rhein-Main and Rhein-Neckar regions, with a bit of Silesia, Saxony and Berlin thrown in. Elsewhere, industrial development came much, much later. Quicker integration might produce faster market permeation and more shocks, shaking up old agricultural and artisan traditions. That, OTOH, might produce a mighty backlash, too. Going quicker with industrialisation would certainly have radicalised Germany much earlier, in both directions.
No German government ever saw the Dutch in this way, though, before the Nazis. And no relevant opposition did, either, before the Nazis and similar Völkische splinter factions in the Weimar era. Even they clearly didn`t focus on the Netherlands much and occupied them primarily for strategic reasons.
You're not answering the question about why the Germans would care about Dutch opinion in a situation where they view them as apart of the German peoples.
And I'd like to point out that no German government was as Blood and Soil as the Nazis. If you get a government filled with radical Pan-Germanists, you could easily get somebody who views the Dutch as Germans, alongside the Danes, Norwegians, and anybody else who isn't French and had significant mingling with the Germans.