1. There are a lot of users that are just not comfortable with working at a shell prompt. Graphical editors mirror the basic Mac or Windows workflow (open folder, double click on file, edit) and key bindings.

2. Syntax highlighting & formatting is better because of support for multiple fonts & better control of color.

3. Integration with other graphical apps. Kate is used as a component inside of many other KDE tools, so when you edit a file, the behavior is consistent and the key bindings are consistent.

4. Better integration with the desktop environment (in this case KDE). For example, I can open a file on a remote machine from the file open dialog. The file open dialog isis keychain aware, and can connect to any host that the desktop environment can (with KDE, that is almost anything that has file-like objects and remote protocol). You can do some editor be able to open a message from an IMAP server like I'm browsing files on localhost.

Kate is more like a Notepad++ or TextWrangler on Mac. It's a solid editor, but not an Emacs, vim, or VSCode level.