Thanks Ged for the gold medal. :) And welcome once again to the fun of being in this awesome community.
The only 'history' that should matter regarding why that documentation is better than any other is that they have been at it dedicatedly, with a fixed purpose for a longer period than any other, towards "marketing" their result of hard-work Opentaps, which is built around OFBiz. I was also part of the Opentaps story for a short period, found it impressive in many aspects but could also see the cracks as I experienced it's half baked features. Fixed several of them while I implemented Opentaps for my clients. Unfortunately, couldn't contribute to having them fixed in the upstream for reasons still "unknown" to be and would be off-topic herein. So back to OFBiz, which IMO has a history of experiments not going its way due to lack of long term collective effort for which I guess we have none other to blame than the community of which I am also a part. (Proof to it being that this is officially my 2nd post only). Off late some of the sleeping giants have woken up and I see every possibility of the much deserving OFBiz gaining more acceptability and an increased user base as there are several things going in its favour as a collective effort. Dig no further about the history and look ahead to build a more productive future. :)