Well the New 3DS has the feature to automatically adjust the backlight based on the environment that you're in. Could it be that when NTR is enabled, it would automatically disable that N3DS feature? Seems like a plausible reason as to why it may have purposely been removed in N3DS models.
Even if that was the reason, i am one of those who really prefer to make these changes manually. If i decide the screen is too bright for me, it isn't exactly like the N3DS would know it is, because everyone has different Brightness preferences, and the N3DS cannot exactly guess my preference.










