For the same reason you don't indent 'else' relative to 'if'. It avoids double-indentation and isn't really necessary. All of the lines under 'case' will begin

For the same reason you don't indent 'else' relative to 'if'. It avoids double-indentation and isn't really necessary. All of the lines under 'case' will begin with one of 'when', 'else', or 'end' and are thus easy to spot without indentation.