I think it is more preference thing, and the factory did the black wall instead as well. I personally do not like the white letters showing on any of my vehicles, but just my taste. Performance tires seem to not have the white lettering as much, at least in the 18 - 20" tires, so a little harder to find now a days too. For example, I have 255/35/20 front tires, just did a quick search on tirerack, and none show the white lettering available. If the tire manufacturers do not make them, then the auto manufactures can not even have the option to install them.
2013 GT 6 spd, GT500 mufflers, BOSS quad exhaust, Roush CAI, Barton shifter & 2 post bracket
CS GT-40 Wheels, Hotchkis sway bars, upper and lower control arms, springs (1.1/1.6 drop) and adj panhard bar KONI yellow struts and shocks J&M caster/camber plates,
BMR Upper control arm mount and lower control arm brackets.