190mm I understand was chosen as a 'compromise' It wasn't exactly 1/10th scale (relative to the chosen wheelbase) but for most cars it was close enough.
Having been involved in the production of r/c bodyshells, I can tell you that even 190mm is too wide for a 'scale' car.
The few that I've done we've had to widen to fit a 190mm chassis. To get them to fit on a 200mm chassis they need to be widened even further.
Basically it all spun off what Tamiya did with their original sedans because that's where Touring Cars started essentially.
We may as well go to LeMans or sports cars now because to call most of the current crop of shells '4 door sedans' is stretching the truth a long long way....
