Open Baffle. Why are they mostly limited to DIY?

Alon, Nola have been around for a while also.  You can build your own field coil speakers and they will sound fantastic!

I stopped into the DIY room at this year's Capital Audiofest and they had a low-powered tube amp driving an open baffle pair of DIY speakers, with a 12" Tannoy driver facing the listener, and an 18" down firing driver for the low bass.
I was really impressed with the sound they produced!  I asked the builder what he had in them and he said "about $1700", and further explained that the only reason the amount was so high is that Tannoy apparently doesn't sell individual drivers, so he had to purchase a pair of their speaker and remove the drivers from the cabinet.
Very impressive sound!  Even more impressive for the price!

I have a pair of Spatial M1 turbo and must say they are not power hungry! I am fan of concentric twitters and I like the bass too ! The only thing with OB is the size of drivers and not very dense sound like high end speakers! I think you should not judge OB speakers if you have not heard any good one!

Yeah I imagine that a lot of sound is lost due to cancellations, unless DSP is used. 

Frustrated with what I hear as colouration from traditional speakers during a 40+ year search for the ’perfect sound’ (including expensive & well reviewed B&Ws, JBLs, Shahinians, Dalis, Royds), I started building Open Baffle speakers during 2012. Last year I finally managed to create something that sounds closer to reality than I have experienced anywhere else.

These are my own hybrid 3-way design based on Pure Audio Project Trio15s & are run as a fully active 5-way system in tandem with twin subs below 50hz, powered by HDP-5 and HDP-3 DEQX processors with multiple power amps. Crossovers, frequency, phase, timing are all handled digitally (although my preferred and most listened source material tends to be vinyl).

Imaging, soundstaging, transient attack and dynamics are simply astounding and I cannot find fault with the speakers, room or system regardless of source material or volume. Well implemented OBs can sound truly remarkable although the lowest bass frequencies remain challenging without assistance.