Meh, its not that there is much to explain by it. The heads are just overall restrictive, valve seat and port size is too small to justify more "length" in the valve opening. Also the valve angle is very shallow which does not promote flow at high lift like a steeper valve angle would.
When force inducted you also run into issues of the intake not needing alot of lift to achieve the same results... Less valve lift and minimal ramp rate is going to give you better real world results by increasing your valvetrain accuracy on sub 150# springs.
ZZP has been there and done the lift thing, its not worth it for power, so now they only sell cams with 550-580 total lift on stock rockers. I was out there in grand rapids when they put 3 different cams in the impala, and it was clear that lift only hurt things, while installation angle actually produced more WHP swings than any other thing we could do in the cam profile (for reasons unrelated to valvetrain I may add, but that is a different thread all together).
So, there is your blanket response, any questions?