Open Baffle. Why are they mostly limited to DIY?

I love OB, but I did find most things, like the Emerald Physics line for example, to be way too expensive and relatively not-so-well implemented for my tastes. So I eventually moved into DIY. I'm currently still building a pair based on Danny Ritchie's "Wedgie" speakers, but attempting to add horns into the mix. Using OB ribbon tweeers and Danny's LGK mids (MMTMM).

OB bass is handled by 2 Hawthorne Audio 15" "Augies", but they are not so much subwoofers here as they are simply part of a 3-way design. Digital crossovers, delay, gain and EQ...(but not phase) all fully adjustable make implementation a dream. Then lots of a singularly good conditioning solution I've found thrown at the whole system that takes the "digititis" and more completely away.

OB bass here is great. It's true that it doesn't disturb room modes or neighbors and that the texture and tone are the best. And as has been said before, it turns the "duhnn, duhnn, duhnn..." of boxed designed bass into the "dahh, dahh, dahh..." of OB - waaay more like real music. When you hear that for yourself, you suddenly understand the underlying reason why it is that 'too much is never enough' when it comes to boxed bass sound and one key reason why everyone seems to be on that endless quest for mo' better bass. When the bass sound is freed from the addition of the "duhnn" sound being imposed onto the decay trail of a deep drum and the sound is likewise freed from the artificially induced dynamic, gut-level "punch" being added to the initial attack of a standup or electric bass line...then the bass instruments are finally and fully 'separated out from each other' and the real sound of each instrument is allowed to come through unedited. Then it can hit you that this level of transparency in the bass can, finally, be made to be Exactly on par with the transparency throughout the rest of the range. Search over. Only the problem of the lowest frequencies remains. Although here that has been far from any kind of deal breaker for me.

Since they don’t disturb room modes would it be safe to say that they are less picky about placement? Or do they need to be loaded in corners? 

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.