Why VI?
Because it can be found on any UNIX derivative OS created in the last 15 years (at least).
Because it's very stable and trustworthy. In case of a system crash, power failure, etc, VI saves backup files that can be retrieved by starting VI in recovery mode (with vi -r <filename>)
Because it does syntax highlighting, automatic indentation, line numbering, has shell-escape features (you can execute other tools from within VI), etc, etc.