Initial quality always seemed like a silly measure to me. I'm more interested in total cost of ownership through 150k-200k miles. Own a GM for 90 days vs own a GM for 15 years and you'll have vastly different results, IMO.
Also, if you wait until you get any substantial real-world numbers on TCO from owners at 150k-200k miles - collecting several years of data - any given car will likely have been redesigned and have a different quality profile. You can extrapolate by manufacturer, but given the extended timeframe it isn't all that helpful - or even more helpful than initial quality - when buying a brand new car.
So you might be interested in mid-life or end-of-life quality, but you can't measure it early in the vehicle's life without an accelerated life test of some kind, and you can't measure it statistically without doing so on many vehicles. JD Power's initial quality survey is just that: A simple consumer survey of defects reported early in the vehicle's life. Hence the name: initial quality.
When you look at how many HF3.6 engine vehicles GM sold over the past 15 years vs how many you see on the road now, reliability (or lack of) becomes obvious. There will obviously be outliers, but the fat part of the curve (in terms of miles at failure) is what is relevant. Even when constraining for things like profile of buyer (e.g. subprime buyers will probably skimp on preventative maintenance), it becomes obvious which companies want to make quality cars and those that are mostly subprime finance companies that happen to sell cars (Stellantis, Nissan to a degree).
This was not our experience with a brand new GMC we had a few years back, which was about as reliable as the previous one, which we got rid of at ~15 years / 250K+ miles. The older one broke down every year or so, but we'd beaten the heck out of it. The newer one experienced multiple major failures in two years, including stranding itself. The old one only stranded itself once through its entire lifespan.
Do you have statistics on that?
I purchased my previous car (a Dodge) when it had 8k miles and had it as my primary car until 240k miles. It only started to have serious maintenance issues at 220k miles. I not only paid it off, but saved enough money to be able to pay for a new car in full. I would recommend to anyone, as it is really nice to not have a car payment.
Also, it's not just cost. Sometimes newer models are just worse. There is one car that I thought about getting a little while ago, but the model changed dramatically 5 years earlier (the older version was what I used on a vacation that got me interested), so I had to look at getting a 5 year old car or a different model.
FWIW, other than one car I bought new, every car I've had I purchased off-lease (so lowish miles and 2-3 years old) and kept it for at least 7-10 years, often getting to 200k miles.
I also would need concrete data to believe most people are swapping cars willy nilly. Based on income/wealth statistics, most Americans most certainly cannot afford to.
The only source I could find said: "The percentage of consumers that are leasing their vehicles has dropped due to the inventory shortage. In December 2021, only 20% of new-car shoppers leased a vehicle, compared to December 2019, when 30% chose to lease, according to Jominy."
https://www.cars.com/articles/how-does-the-inventory-shortag...