They just suck, that is all. If you had a working trunk release from the factory all they would have to do is tap into that wire, even if they had to follow it back to the trunk itself. But here is the info on the trunk release: Black/White (+) Switch or Brown Passenger’s Relay behind Glove.
They just plain out suck, I worked for Ziebart YEARS ago for about 2 weeks and quit. Their quality of installers is questionable and their volume mentality sucks. I would call them and complain and tell them to do it right.