They actually gave them a loophole doing the exact opposite, vehicles with a bigger footprint had less strict mpg requirements.

This was written in 2011:

CAFE standards create profit incentive for larger vehicles
The current Corporate Average Fuel Economy standards create a financial incentive for auto companies to make bigger vehicles that are allowed to meet lower targets, according to a new University of Michigan study.
…
The loophole is the formula for setting mile-per-gallon targets. The standards, which actually depend on the sizes of vehicles automakers produce, are expected to require that firms boost average fuel economy to 35.5 mpg by 2016 and 54.5 mpg by 2025. Those oft-cited numbers are averages. In reality, each car company must meet a different standard each year determined by the literal “footprints” of the vehicles it makes. A vehicle’s footprint is its track width times its wheelbase.
According to the study, the sales-weighted average vehicle size in 2014 could increase by 1 to 16 square feet
https://news.umich.edu/cafe-standards-create-profit-incentive-for-larger-vehicles/

Apparently decreasing sales, but half a million Buicks sold in 2023, plus the whole: “GM China sales decreased nine percent to 2,098,980 units during the complete 2023 calendar year. Sales decreased at all five brands marketed by GM in the Asian country, including Buick, Chevrolet, Cadillac, Baojun and Wuling.”
https://gmauthority.com/blog/2024/02/gm-china-sales-figures-numbers-results-2023-calendar-year/

At that scale, it would be extremely embarrassing if GM can’t stay competitive & profitable.