The command line works until the first time you choose a view from the menu. When you exit, that choice gets written to cfg\vectrex.cfg and the command line doesn't override it.
If you remove the view="xyzgame overlay" part of the target line in the video section of the cfg file, the command line view selection will start working again.
You can remove just that entry, the whole line, or delete the whole cfg file, depending on how much reconfiguration you want to do. For example, if you had turned the crosshair off within Vectrex, then deleted the cfg file, you'd lose that setting too.