Apple rejects such apps because they use private API calls. These API calls are part of the Electron framework and are not in the app.
The Electron framework has been using these APIs for several years, and Apple has recently updated its service-side application review process to detect and identify private APIs that violate their app audit ingress.
Electron (formerly known as Atom Shell) is an open source framework developed by GitHub. It allows the development of desktop GUI applications using Node.js (as a back end) and Chromium (as the front end).
Electron is now used by several open source Web applications for front-end and back-end development, including GitHub’s Atom and Microsoft’s Visual Studio Code.