Final answer:
Municipal legislatures grant zoning changes because they are responsible for creating and amending laws that guide land development in accordance with a comprehensive plan and public welfare.
Step-by-step explanation:
Zoning changes are usually granted by municipal legislatures because the legislature made the law, so it must adopt changes. This responsibility is part of their role in land-use administration, which includes the creation and adjustment of laws to shape the development and use of land within the municipality's jurisdiction. Additionally, zoning ordinances must be reasonable, protect public welfare, and be in accordance with a comprehensive plan, typically reflected in a master or official map that outlines future development.