30-odd years ago I knew one person who drove a dual fuel car - today I don't know anybody.
It may cost over a grand to retrofit LPG as dual fuel but for a manufacturer to fit would cost considerably less AND make the car more attractive to many punters.
The number of refuelling stations has grown VERY slowly but if cars had the dual option from day one then every forecourt would get their act together pdq. If I had to drive 10 miles to fill up with gas I'd most likely fill up with diesel at the same time.
As for manufacturers warrantying home-made fuels, Fiat told me they were happy for me to run my dobby on a 5% veg / 95% diesel mix - so why not add a small tank to the rear 1/4 panel that is insulated and can be filled with pure veg oil - again, installing from the off would cost a fraction of a retro fit &
having the dual fuel facility would make the car more desirable. having this facility in all the oil burners would encourage the forecourts to sell biodiesel (certainly encourage someone to take the reins). Again, it is supply and demand. there are so few diesel drivers willing to give it a go
that large scale production isn't viable.
As for the warranty - it wouldn't be too difficult for them to test if pure veg oil went in or something that was used for Bhajis yesterday.
As for the towbar, again, a retro fit cost me £100 and the equipment I got was a simple metal bar to replace the existing bumper bar plus the wiring which could be scotched into place - although there is actually a plug especially for this in the loom.
And yes, not everyone wants to tow but Vauxhall introduced one of their cars with a nifty bike rack built into the bumper - who the hell wants to ride a bike when you have a car? - but they obviously thought it worth trialling.
The thing with manufacturers fitting stuff is that it is bound to be much cheaper as they have purchasing power & to fit something as the car is assembled would be far cheaper than a retro job.
I've driven a few things recently which have a small device by the driver which allows me to adjust both door mirrors - why? As the driver I only need to get them right once & i can ask a helper - it's worked for many years. so fitting a fully adjustable mirror system is a very expensive waste of money. But it is a selling point - just as many other things are.
Personally, I would rather lose some of the luxury and have more economy.
I am more than aware that i can spin up my turbo and beat quite a lot of cars off the line but just in terms of mpg, I am a little worse off now than 20 years ago when I had a pug 2.3 diesel. In terms of performance, 0-60 was measured on a calender
Argonought is correct that the main drive is money rather than environment, although I'm not really sure that any of them are concentrating on squeezing more economy out of their cars as those figures always seem to be in small print