Mystara is a setting that grew out of the merging of various components such as the Known World, the Hollow World and Blackmoor. What these components had in common was that they were all linked to the Classic D&D rules instead of AD&D. But there was already a Blackmoor in the AD&D Greyhawk line. Why would TSR want to present another Blackmoor? In 2012 Frank Mentzer revealed the following:
"[...] We all remember the tussle between Gary and Dave
and its effect on certain developments in the game, editions, etc. Once that was settled* (which was in the early '80s, during my time there), we discussed options. Since the World of Greyhawk included Blackmoor, should it go there (AD&D1e)? Or since I was drawing from OD&D & supplements, should Sup2 (Blackmoor) go there? Anyway, it ended up in BECM, as you know.
Once the executive decision for placement was made, tho, it was handled by others; I was too busy to do modules (except some RPGA tourneys on the side) or Gazetteers. Given the importance and nature of Blackmoor -- the first fantasy campaign, to some -- it got its own line, instead of being a 'mere' gazetteer.
* In actuality iirc 'settlements' were reached at 3 separate times -- late '70s, early '80s, and then later '80s with the PoG, post-Gary -- before Dave was finally happy with the whole shebang.
Time for my usual caveat, which I haven't offered for a while. All of these and other reminiscences are, and ever shall be, 'If I recall correctly', and I may be in error on various technical points, precise dates, and such.[...]
Apparently, Blackmoor's return was the result of Gary Gygax approaching Arneson. In spite of their differences, Gary must have realized the significance of Blackmoor and also likely believed it could have commerical value. The result were the DA modules.
The DA modules and later also the Gazetteers suggested that Blackmoor existed thousands of years ago. They were vague on its exact location, but seemed to suggest that it was located in the same region as the Known World would later appear. This was problematic from the beginning as locations didnt match up and was made further complicated when the Golden Khan of Ethengar suggested that the Steppes of Ethengar were the North Pole during the Blackmoor Era. Then the Hollow World Boxed Set came out and placed Blackmoor on Skothar, another continent. At the Piazza today, Bruce Heard explains why some of these decisions were made:
"I had to move it out of the Known World because of design contradictions and, basically, no good place to put it. It was relegated to Skothar which was essentially a blank area. Blackmoor was interesting but really not well integrated with Mystara. Management and marketing wanted to have Dave Arneson's material attached to Mystara because or their common connection to Basic and Expert rules, and so the non-negotiable "request" came down to accommodate Blackmoor. The whole thing was well-intentioned but terribly awkward. It should have been designed from day-one to fit Mystara and not pretty much slapped onto it."
Of course, us fans have been taking care of that last part.
Full version here: http://blackmoormystara.blogspot.com/20 ... stara.html