Why so few high end line arrays?

To me the intrinsic "wall of sound" of this design are compelling. I recently tried a very nice 3 way w/ stereo subs in my system after 2 years of line array-only listening and the lost impact and scale of eight midbasses/ribbons per side was profound. I was immediately aware of the music emerging from boxes, despite very nice imaging. And it's not that the arrays exaggerate the size of voices and instruments. Does the materials cost dissuade manufacturers? Is it the size? Seems like relatively unexplored territory in high end home audio.
After hearing some outstanding line arrays, I totally understand why people like them. I am about to get a just released line array from a manufacturer for an audition. I was worried about combing as well, but the drivers are small and quite close together, so I suspect at normal (not nearfield) listening distances this should not be a problem.

I'll post back in a few weeks with some initial thoughts, but at 16 ohms, (perfect for my OTL's) and no crossover, I'm thinking this might be an ideal speaker, (for me anyway).

I use Atma MA-1s with mine and the arrays are custom wired to yield 13 ohms nominal, 10 ohms minimum. I wasn't prepared for the difference that proper impedance matching makes with OTLs. You are likely in for a treat.

As for comb filtering, diffraction effects manifest in all manner of speakers - even single driver/baffle interactions occur. Not unlike our listening rooms themselves.

It is what we perceive that matters. I hear the bass nodes/nulls in my room quite well, ameliorated as best as possible with traps and PARC. Comb filtering in the "line array physics" sense is imperceptible in my setup. FWIW, I sit 10-11 feet back.
There is another approach that is worth considering - The Genesis Horn from Danley Sound Labs. In essence Danley's interpretation of a line array http://www.danleysoundlabs.com/pdf/GenesisHorn-anewbeginning.pdf
As for all line arrays, you are going to need a large room. It is pro audio so it needs a face lift if in the home environment and on display.

Thanks for the response regarding higher impedance speakers. I currently use a Zero autoformer to raise my current 4 ohm speakers to 8 (anything higher than that and it didn't sound right)

Your system looks great as well.