The Geany project does not make packages, each platform has its own rules and often patches to fit into. The project does not have resources/expertise to support all platforms.
But the project does make a [Windows installer](https://download.geany.org/geany-2.0_setup.exe) which bundles all the required dependencies (GTK etc) and IIUC is based on msys. This is provided by one person and its unlikely that they will have the effort available to support another windows package.