Obsidian desktop is developed by using [Electron](https://www.electronjs.org/). And Obsidian mobile is developed by using [Capacitor](https://capacitorjs.com/)
Technically, the plugin (or any plugin?) runs in the js environment provided by Obsidian. And to support the mobile Obsidian, the plugin is limited to be developed for the browser environment, instead of the Node.js environment.