I would say that most likely it's because such an intake would have rather short runners. This would make it work well for high rpm but in most applications it would probably be out of tune at any reasonable engine speed with the larger engine.
Some years back at SEMA I had that conversation with two guys from TFS when I told them I thought they should build a T/R designed for a 400" Windsor with good heads 320 CFM's and a power range of 7,000 but build it with room to port for guys who want to build a bigger engine or rev it higher.I'm sure that's a BIG part of the total picture, weather or not you can sell enough copies to make the development work and tooling costs even break even.
That's the REAL spirit of "hot rodding" ... Make it, don't just buy it.maybe I will have to buy a tig welder this winter and build my own. Who's got the best price on a decent tig welder for home use? I made everything else on the darn car.