This is especially weird because the Netherlands does not normally permit dual citizenship.
It seems like many (most?) countries don’t like/recognize dual citizenship. The way it ends up working is that each country doesn’t have the power to tell the other country that someone isn’t a citizen. Each country just enforces it’s own citizenship within it’s borders. If you had US/Netherlands citizenship, and use a Dutch passport to try to enter the US, you will probably get yelled at by customs if they realize that you are a US citizen. They can’t stop you from entering the US but they can hold you for a while and pester you.
If you have a US citizenship but live in another country, most of your income will be exempt from US taxes (unless you are a millionaire, in which case you probably aren’t paying many taxes anyway).
A similar thing happens with countries that have mandatory military or civil service; you can be required to travel back to serve.