Stop and go traffic jams aren't completely automated by most ADAS systems. For one, you're still completely liable for it failing. Secondly, most of those lane keep assists will still let your car wander out of the lane if you really don't pay attention, they mostly just tug at the wheel to help you notice drift or will beep at you. Finally, a lot of those will require manual intervention for it to start moving again after a full stop.

Mercedes implementation takes the legal liability. It will definitely stay in its own lane without any driver input. It will continue going again after a full stop all on its own.