Browsers(Chrome/Safari/Firefox) on iOS(in some cases, including Androids also) have been missing some features of nowadays modern javascript (like ES5, ES6, ES7…)
Electron(chromium) is usually regarded as the main target browser of this MagicMirror, so supporting compatibility for other old/limited browser is not so easy to decide. For example, new features like arrow function, Promise, Set()/Map() could make developers apply better features to their modules easily. But some old/mobile browsers cannot support those features.
Maybe a good developer can make his module fully compatible with all browsers and platform, but probably codes would be somewhat complex or dirty. Has it worthy? Maybe too. But that effort could not be the duty of a volunteer.