Hi Bob,
I reckon part of the reason is that the various fuel economiser devices you mention need a master-tinkerer to operate them.
Big Auto has to sell vehicles to folks that are totally ignorant of how the vehicle works, couldn't tweak or adjust nothin' and would screw it up if they tried.
Heard that back in the day the original Austin Mini sold big on the West Coast to ladies who really liked it's economy and small size.
Except this one lady kept bringing hers back because it was a swine to start, didn't run well and drank gas like a fish.
Time after time she brought it back and they couldn't find the problem.
Finally the sales manager said OK lady, this time YOU will drive and I'll come with you.
The starter grinds and grinds, the accelerator gets pumped and pumped and it takes three minutes to fire up.
See, she said, now will you agree that it's a swine to start? Now I'll show you how badly it runs.
But first she said, pulling out the choke knob and hanging her purse on it, I must say that I DO like this little feature.
It's folks like that you gotta sell cars to.