The standard factory brakes are horrible. On my old 2016 Denali I only got 16,000 miles out of the first set of front pads and rotors. By the time I got rid of it at 36,000 miles it needed another set (and the second set had the "heavy duty" GM pads.
I'm sorry but you must drive like a lunatic just punishing your brakes. I'm at 49K on my 2015 Denali and I have ~50% of my pad material left. I'm a car enthusiast who likes to drive spirited (also own a 2018 Audi S6 and 2002 Corvette Z06) so my driving style isn't exactly subtle. I also realize the Denali isn't a performance car or track weapon so I don't treat it like it is. I drive to Colorado yearly through the mountains, tow a trailer occasionally and deal with Chicagoland traffic so my brakes see their fair share. You gotta be pounding the tar out of your vehicle to be killing brakes inside of 20K intervals.