Why not more popular?

My only experience with open baffle is my current speakers which are GR Research NX-Oticas with dual 3-stack OB servo subs.

Admittedly, this is a large system which won't fit in many listening rooms, but it certainly doesn't suffer from any limitations in the lower-midrange and bass regarding weight and authority. These have, by far, the best bass I've ever experienced in my own systems which have included some fairly nice box speakers from Revel (Studios with Ultima Subs) and Duntech (Sovereigns). 

I can certainly understand why the GR-Research products are less popular because they are DIY "kits", and are more difficult to sell when you're ready to move on to something else. But I've read a lot of good reviews of other OB systems, particularly from Spatial. From the reviews, these seem to have good bass performance, but I could be wrong. 

I've heard good things about the GT Audioworks and Diesis speakers as well, but these are priced beyond most people's budgets. 

As I noted in my OP, I've owned a few Magneplanar speakers and always like the presentation, but these did lack in dynamics and weight for my taste which is why I never stuck with them for more than a few years. But that certainly isn't the case with my current speakers. 

@mijostyn - I think an H-frame or W-frame design works a lot better for open baffle since it keeps the baffle size very small (barely bigger than the driver). My cabinets hardly vibrate at all (less than the sealed Velodyne subs I use in my home theater) and sound very natural to me. 

I have open baffle subwoofers that sound fantastic in my room. They seem to have way fewer problems exciting room nodes than conventional sealed or ported box designs. Probably similar to what can be accomplished with a swarm, but without "pressurizing" the room. The bass sounds more natural than I've heard from box (sub)woofers - I think because it is creating bass more similar to the way an instrument does. 

Using Room EQ Wizard, There are a couple of very narrow nulls at the listening position that are about 8db down due to room nodes, but 1/12 octave smoothing gives me response that is within a couple db from 18Hz up. 

My sub towers aren't small (three 12" servo controlled drivers per side), but the bass performance is worth it to me. 

https://systems.audiogon.com/systems/8726

I remember the DQ10 fondly, although I agree that the bass was their weakness. 

I haven't heard other full-range open baffle designs besides the ones I currently own. But I can say that the bass is definitely not a weakness in these speakers. I think the combination of drivers specifically designed for open baffle, plenty of radiating area, and servo control, really brings it home. 

But I will agree that this requires considerably more space than a conventional speaker. I have two large cabinets for each channel, and they absolutely can't be pushed up against the front wall. I'm fortunate to have a big enough dedicated room to let them shine.

From what I have heard from others, the Spatial speakers deliver excellent full-range performance in a more room (and WAF) friendly implementation. 

@bdp24 - thanks for adding all the detail. Danny's OB subwoofers are also used by GT Audio Works to great effect. These systems have received considerable praise at various audio shows over the past few years. 

The company that Danny worked most closely with that used the  Bohlender Graebener drivers was Serenity Acoustics. The company that acquired BG significantly reduced availability of the drivers (they used them in their own theatrical and pro sound reinforcement systems), which forced Serenity out of business. 

The specific models that I'm familiar with used the BG NEO10 and NEO3. Danny has been able to develop his own NEO3 replacement, which he uses in a number of his products, including the NX-Oticas which I currently own. He is also trying to create a replacement for the NEO10, but so far he has not been satisfied with the results of his prototypes.

Parts Express is now sourcing a similar driver to the NEO10 (and NEO8), but this driver does not measure as well as the BG NEO10, and also doesn't play as low in frequency, so can't be used as a substitute in Danny's Serenity designs. 

The Serenity Super 7 (which used a pair of 12" servo subs, four NEO10s and one NEO3) sold for $20,000 during it's short market life (before Serenity went under) and was (is) well regarded.

The Serenity Line Force, which used 6 NEO10s and 16 NEO3s (for each channel) in a line source configuration, along with a separate subwoofer cabinet with configurations of 2 to 4 12" servo drivers, was only shown in prototype form at shows, and used a machined aluminum open-baffle cabinet. It was expected to sell for $40K to $50K. 

Danny has continued development on both these models (when the BG NEO 10 was still available through Parts Express) to adapt them to use his NEO3 driver. The Line Source cabinets were re-engineered to use a composite material instead of aluminum which has reduced the machining cost considerably (although they are still quite expensive to produce).

I have been lucky enough to acquire enough BG Neo10 drivers from Parts Express before they became unavailable to build a set of Line Forces. I hope to have them completed later this year. 

@tomcy6 - Clearly not just DIY. There are a few well regarded brands. But this is a tiny fraction of the number of box speaker brands, and most audio stores don't carry any. In fact, most audiophiles that I have talked to have never heard an open baffle speaker system (at least knowingly), which is why I posed the question.