It's not necessarily about large file size (storage is cheap anyway) and memory usage (although RAM on portable devices is still kind of limited).

Performance in Electron-based editors (e.g., Atom) is horrible. When you're used to vim or fast GUI-based editors like Sublime, even typing in Atom feels sluggish. That's not even talking about loading large files, search-and-replace operations, multiple cursors, etc.

Example stats: https://blog.xinhong.me/post/sublime-text-vs-vscode-vs-atom-...