Go take an hour's drive around any rural or urbanized community. Count the more modern vehicles (less than eight years old)...divide them into the category of sedan, truck, SUV, or crossover. The bulk of cars you see fit into trucks, SUVs, or crossover vehicles. Where you do find sedens....it's high-end type....sporty models....Asian models (Japanese or South Korean), or normal US-made sedens driven by folks over the age of fifty.
GM set up a strategy and stuck to it.....the customer base? They went to something else over the past decade.
When they did try to build a seden.....they scored marginal point with pieces of crap like their Impala model (loads of noise, jolts on every bump, poorly designed seats, etc).
If you went to some eighteen year old kid who will graduate this year from high school, and they'd like to get a new car for college coming up.....it won't be a US seden.
Should they have realized this impact back around 2010? I suspect that the statistical crowd was telling them every quarter that they had a problem, and they refused to change their strategy.