Because the light control module can detect when a bulb goes out due to a drop in load on that circuit. LED'* don't quite have the same load value and will confuse the module.

And, depending on the vehicle, if it believes a bulb is out, it may disable it, which would cause a whole new problem.

there are some LEDs that may simulate the load, but use those at your own risk, assuming they even work.

Thanks. I used error free LEDs in my '17 Ford Escape and had no issues so was just curious what GM meant by "possible electrical issues." Certainly don't want anything to get fried.