Using - before the column name is only applicable when sorting by multiple columns at once. e.g. Set SORTBY=-name,size
When sorting by only one column, only SORTREVERSE is what defines which way around the sort happens. (SORTREVERSE works with multiple columns as well, reversing the overall order.)
If you are already sorting by name, in either direction, then Set SORTBY=name (with or without the - before the column name) won't do anything as you're asking it to something that's already being done. But if you were sorting by another column, it will change to sorting by name.