It's a stipulated requirement in most cases but enforcement of rules for employers is massively underfunded, so companies that don't have to deal with a union aren't bothered that much by regulations.
Government workers are well organized and don't notice that the rules they thought up (and are responsible for having enforced) actually are ignored by most non-government employers.
In fact, government is usually calling for a more flexible labor market, even though the Dutch labor market is among the most flexible in the EU (if not the most flexible as, again, any costs to getting rid of employees in an illegal fashion are neglible in the first place. They are also not enforced at all unless the illegally fired employee has the wherewithal to sue. Which is not trivial for lower paid people as access to subsidized legal help has been slashed. And even if you have a fixed term/hour contract, no country has as many temps and contractors which can be shown the door by the people paying their fees, which leads to unhealthy power dynamics with their immediate employer as well.)
So yes, in theory (and for government workers in practice) it's all nice.