Probably true that the technology or software is not supplied to towbar fitters. Keeping it in house adds to profits especially if it goes wrong at some in the future point.
It could be a of lot less "evil" intent and simply to keep within mandatory dictates and fend of the hurt of any legal claims, that might spin out of non compliance of a host of international regs, or third from party post build intervention?
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In the push to ever more efficient & greener vehicles, it surprises me the number of domestic car market vehicles that are still built with integrity reserves to not only cope with say five people and the carried luggage, but additionally tow trailers that can double the mass lugged about, controlled and stopped.
I just think it is way over designing, and we are sure to see domestic cars designed "just" to be that, not also a tractor. You don't end up with the most efficient solution, or cost effective solution by adding in additional capability, let alone expect it to cope with doubling the mass .
I therefore see there has to be a move to produce factory option vehicles, based on the standard product but where they are modified to tow trailers. This, rather than expect those not factory specified to tow, in later life being converted to tractors, the more so by third parties.
The huge pressures from China on Western domestic car manufactures can IMO only speed up designing vehicles to be just adequate. I suspect that in the future less and less domestic market cars will have the integrity in the bulk of the componentry, to ever be offered as tow cars, even as an option.