Open Baffle. Why are they mostly limited to DIY?

Open baffle speakers must be a nightmare to design (bandwidth and cancellation) otherwise they would render all box speakers obsolete.

The problems of getting cone drivers to work perfectly in a box are infinite. Box speakers will always be flawed though some try very hard - Harbeth, Wilson, Magico Fujitsu Eclipse etc. 

seanheis1: Many OBs need space to breathe and should ideally be kept well clear of front and side walls.

One other comment about bass & the reason I use subwoofer reinforcement below 50hz:
Much live music is amplified through horn or box speakers so we often don’t hear vocalists or instruments ’naturally’ anyway. Even using four 15" OB drivers as I do, this cannot recreate the depth of live sound or indeed something as subtle as a foot stomp on some solo acoustic albums. OB bass gives the speed and transient attack of real instruments and correctly blended sub bass the final sense of realism.

From the standpoint of room modes they're less picky about placement, but they do need room to breathe away from the front wall of course, like 3-5ft out into the room. Corner loading is not particularly necessary normally, but corner loaded designs could be good.

I think what most people who don't have that much experience with OB bass tend to assume about it is that somehow the OB bass sound is dialed back or deficient in all areas across the board...that the whole bass output is insufficient in all areas, or that the lack of low end is egregious - it isn't. It's only lacking compared to other designs when it comes to low frequency extension **given the same woofer diameter of boxed designs** IOW, If you are looking for a certain low frequency depth compared to 8" woofer in boxes, you might need to be looking at 10" woofers to get a more directly comparable LF extension in OB. Or, for LF extension of 10" boxed woofers, you might more directly compare to 12" OB, and so on. Otherwise, well implemented OB bass is just as dynamic, punchy, forceful and has about as much slam as boxed. Maybe the only other catch is that it's rather necessary to only use drivers that either happen to be suited to OB use or were specifically designed for OB use to start with...of which there are still not all that many...to date, anyway. Other than that, they are not any harder to design, really. In fact they are easier overall.

Why they have not yet caught on like other designs (but seem to be steadily gaining) may have more to with non-listening related factors, I suspect...WAF and the need to be placed out into the room and so on. But, they make an excellent choice for a dedicated room for example, and IMO sound-wise they are underrated when well implemented...but then again, I suppose about any speaker is underrated when well implemented.

Open baffle speakers must be a nightmare to design (bandwidth and cancellation) otherwise they would render all box speakers obsolete.

They really are not that hard to design. But if you want to do it right, they are going to take up some space, and unless carefully built, the WAF is not as good as 'ye olde box'.

The ultimate "Open Baffle" system involves simply hooking up "raw" drivers and giving them the freedom to bounce around on the floor unattached to anything but the wire from the amp. Anything else is simply baffling.