You mean short of supplying +, -, to the gauges, various bulbs, (illumination, high beam, turn signals, check engine/choke, 4wd, brake, plus idiot lights if not gauge equipped) and carrying the output of the various senders/sensors to said gauges?
I'm sure GM did it partially because it's a good way to cut down on clutter, wiring hassle/expense, maintenance, and how deep the dash needed to be. Nothing at all wrong with PCB's, think of one electrical device that doesn't use one. (well, ok, one that doesn't use a circuit board of one type or other) Not to mention every GM vehicle I can think of, 1970's into at least the 1990's.
A single connector into the back of the cluster makes more sense than 18 wires terminating in seperate locations.