For years was a vacuum controlled cruise system, a rather complex mechanical device with clockwork that had a mechanical memory for speed. Long cable to the carburetor to advance the throttle, and was in series with the speedometer cable for vehicle speed data. And had vacuum lines running all over the place, to both the clutch and brake pedal for quick vacuum release, plus electrical switches as well.
Then the came out with an electronic servo controlled motor, and used the Vss for speed control, still rather complex, because still ran a cable to regulate the vane in the throttle body.
Vss stands for velocity, what it is, is a tiny bar magnet with a few turns of wire on it, called it a ten cent part, has a toothed gear in the output of the transmission that fires pulses proportional to vehicle speed.
It was first used for automatic transmission control, early transmissions used a very expensive mechanical governor, modulator, and a rather complex control valve assembly. a hail of a lot cheaper to use an 89 cent microcontroller, activate four solenoid valves to do the same thing, Cruze added a couple more solenoid valves for six speeds.
Speedometers were expensive, a mechanical tachometer with a bunch of gears in it, ran by the speedometer cable with more gears in the transmission. ECU is already there, can received multiplexed signals. so used the Vss to trigger it, and used a cheap voltmeter that is now your speedometer that is a hail of a lot cheaper to make than that tachometer. But the tach does not show engine RPM but is calibrated to read speed. Vss already there is also used for the cruise control, so now serving three functions instead of just one.
Throttle linkage, all mechanical was also expensive to manufacture and even install. Just put a cheap potentiometer on the gas pedal and a cheap motor on the throttle body vane and just run a wire. So rather than having that servo motor and its circuitry look at that potentiometer on the gas pedal, have it look at circuitry already there for the Vss. Speed is stored in dirt cheap ram, already has the D to A converter to control that servo motor.
So just saying, only cost a couple of cents to add cruise to a vehicle. Just need some more ram, and some switches, guess who left off the switches in the LS.
Inventory is profit according to the IRS so require certified CPA's to count it, this in many cases cost more than what they are counting, so is actually costing GM to leave the cruise off the LS than to just leave it in. This is a marketing decision, a bunch of greedy basterds, to encourage the buyer to purchase a more expensive vehicle, but just can't get the cruise, have to buy a bunch of crap with it so you even have more problems.
Just telling you the way it is. Greed.