Although Maastricht cannot submit a city law, it must have been the case:
The Duchy of Brabant was highly urbanized by medieval standards. An extensive power dynamic developed between the dukes and these cities. If the duke was in a vulnerable position, for example due to dynastic problems or military threats, he could "buy" the loyalty of his towns and villages. He did this by giving them city rights, tax exemptions, or other privileges. This was advantageous for the (new) cities because it meant legal privileges for the inhabitants, for example.
Tax and toll privileges were good for trade. In this way, cities such as Leuven, Brussels, 's-Hertogenbosch and Antwerp could grow into the most powerful cities of the duchy, with a flourishing trade. The duke could then use the wealth of the cities to borrow money, which in turn was accompanied by the granting of new privileges.