For the simple reason that when I first started breeding rats for feeders I bought rats at our local petstore....not because oooooh that one looks pretty....but because that was all they had in the sizes and sexes I needed.
Secondly, I think I can fairly say that not everyone on this board is so well versed with rat markings/colors. Should we be? I'm not sure. I strive to make sure all my rats are healthy and are producing heatlhy litters. I don't know the differences between many of the "high white" genes your talking about. Most information I have I recieved from here through links and discussions.
It's not my intentions to breed "pretty" rats, so what are the rats you recommend that can be safely bred?