Higher Build Height in Nether & End

Since 1.18, the build height has been changed in the overworld, and I thought; why can't it be the same for the Nether and End? Can't those dimensions have increased heights? I just thought because it wouldn't be very hard, all it is is extending the build height from Y256 - Y0 to Y319 - Y-64. Forgive me if I have this wrong and it would be an excruciatingly hard task, but I just think there isn't any reason not to add this in.