People and companies do switch when it makes sense to. Detroit is as "flyover" as you can get in USA, yet American cars went metric decades ago, because it made sense.
Are you sure about that? Across the board? Last time I worked on a Ford truck, the driveline was imported and metric, the chassis was domestic and SAE. In order to remove the transmission, I had to have SAE tools to remove the rear crossmember and metric tools to uncouple the transmission. But that's just a practical example, let's not let facts get in the way. It's been a few years, maybe the chassis department has changed. Maybe it's made in Mexico like so many other cars/trucks. For the F150, the most popular vehicle in the US, it is mostly made in the US.
As you sure that the domestic performance engines are metric? I kind of doubt it. There probably aren't any imported components on the Chrysler Hemi. But I don't know that and I don't know how to find out. Maybe take a 9/16" wrench to the showroom. Unfortunately, a 14mm wrench is nearly identical.
I'm pretty sure NASCAR, including Toyota, are using SAE because the aftermarket parts are not imported and unlikely to be metric. Interesting fact, NASCAR Cup cars must use pushrod type valvetrains. Toyota doesn't make a production engine with pushrods so their engines are not derived from any 'stock' car. They shouldn't be allowed in NASCAR but here we are. Of course, NASCAR has drifted so far from 'stock' that they really should change their name.
The auto industry, indeed any industry, can convert to metric any time they want but the US, that is, the people, aren't going to change along with them. The topic is "why is the US not Metric" and it has nothing to do with the auto industry. The US itself is still using customary units and will for the foreseeable future.
If there is a business advantage to converting, business will do it. The shareholders will insist! But when the workers go home, they still buy beer in customary units (bottles and six-packs).
There is no reason for metric in the things that most affect people's lives and that's why we haven't changed and probably never will.
For all the good reasons posited, and they come from the same playlist created 50 years ago, we haven't budged. And we won't...
To prove that last point, look at the total lack of success with metric road signs, something that does impact people's lives. That experiment didn't last long!
There's only one road in America with just metric markings and that runs between Tuscon, Arizona and the Mexican border. Not a highlight of our freeway system. It's 63 miles or about 100 km long. The only one... And, even then, they had to do distance to off-ramps in meters and other distances in km.
I'm surprised it hasn't been changed back to customary units. Why spend taxpayers dollars confusing taxpayers?
https://www.cnn.com/interactive/2015/07/us/metric-road-american-story/''I hear that the meter is based on a rod somewhere outside of Paris,'' Wolfe said, according to the Times story. ''To use that as a basis for measurement is completely arbitrary and intellectual. I should say I have tremendous admiration for the French, but a matter of this importance should not be left to them. I like the idea of the foot - as a measurement in relation to the human body.
Seems like I'm not the only one that feels that way. It's an interesting article.
Not that it's relevant but the Ford F150 truck is the best selling vehicle in the US and has been for 36 years.
https://www.businessinsider.com/ford-f-series-f150-truck-sales-record-history-2017-1