I am actually from one of these places (Steenwijk, Overijssel), so while this isn't my usual area of expertise I feel confident enough to contribute.

Allow me to get the obvious out of the way first. The (modern-day) Netherlands is an extremely flat country, with often waterlogged soil. Due to the geographical challenges you'd be hard-pressed to create a classic hill fort, for instance, anywhere beyond perhaps a few locations in the southeast.

Bastion forts, therefore, were a more manageable solution. They provided the oversight required to effectively defend a town situated on a flat plain.

The particular penchant for star forts is as much timing as anything else. This design started spreading in the mid-1500's. The last big provincial wars, the Guelders Wars (1502-1543), had just ended by then and through the Habsburg Netherlands the country was more united than it had been in a long time. Right in time to rise up against Spain in the Eighty Years' War (1568-1648).

In the years of relative peace in between those two, and of course in the ramp-up to the war and during the twelve years of peace (1609-1621) in the middle of that war, town defences were re-updated according to the latest design most suitable to the Dutch landscape, which happened to be the star forts. The way this war was fought, with the Spaniards bombarding the everliving daylights out of any town in their path until they managed to occupy them, made these fortifications commonplace.

When the war ended with the recognition of the Dutch Republic, it was also close to the end of battles fought on what we would currently consider Dutch soil for a long time.

All of this coincided with the Dutch Golden Age. Jonathan Israel marks the early Golden Age as 1588-1647 and the late Golden Age as 1647-1702.

The colonies brought in money, and were also the primary ground for any conflict, alongside the water. This allowed for the star forts in the Netherlands to be well-maintained even as towns grew and in some cases sprawled over them. Bastion forts remained a good design choice, especially in the Dutch landscape, so there was no reason to get rid of them. Especially since they represented a significant investment.

By the time significant land-based conflict rose up again, centuries later, the old defenses had been absorbed into the town layout and were (and still are) valued as a part of the "historic center".

To defend the area from France and/or Spain and/or Habsburg Austria. The beginning of the period in which star or bastion forts were useful and being built also coincides with a series of wars between the Spanish, Austrians and French that were partially fought on Dutch soil as well as the beginning of the wars of Dutch independence. The region is pretty much flat and aside from a few rivers it offers defenders little in terms of terrain advantage. Artillery had also progressed to the point where medieval-style castles with upright walls and rounded towers were nearly if not completely obsolete. So existing castles and fortresses were upgraded and new forts built to plug the gaps in the line.