Single Plane or Dual Plane? The Great debate!

I would like to ask a question.

When we talk about port velocity and volume and the effectiveness of each application, it brings up a question I always want to ask...

It reminds me of David Vizard's writing about using DIFFERENT size valves on four valve engines- say ford's modular 4.6/5.4 he compares using different size valves ( PolyQuad) to being as effective as variable valve timing. {page118 how to port & flow test cylinder heads}

-So if this is SO effective with "reduced fuel consumption and emissions, more low-speed output, and better top -end horsepower -

Why doesn't anyone run multiple (alternate size)small intake runners instead of one big fat one for each intake runner on the intake manifold?