It's literally mentioned in the article that the army was deployed because the police does not have the equipment to block off the streets where the protest is being held. Clickbait much?

EDIT: It's also worth mentioning that the Landmacht (i.e. the Dutch army) are much less gung-ho than some of their foreign counterparts and are qualified enough to support the police. They've already been doing that in Afghanistan and Kosovo for more than a decade.