Are you sure they are on?
We've got a '23 Traverse with the tow package and I was showing my wife the hitch guidance. When the backup camera is on ours has three icons at the bottom.
The middle one changes the lines to just a straight line to align with your trailer.
The one on the right shows a downward view for when you get near the hook up point.
The one on the left takes you back to the normal park assist lines, BUT it also acts as a toggle to turn the lines off and on completely.
I learned this when I accidently turned off the lines while checking out the towing stuff.