A Tale of Two(?) Dungeons

In the comments to last week's post about The Official Advanced Dungeons & Dragons Coloring Album, an anonymous poster theorizes that "the map used here is identical to the one in the Holmes basic set intro adventure" to which commenter Frank replies that it's "not identical, but very close." In the interest of discussion, here's what the Holmes Basic Set map looks like:

Meanwhile, the map from the Coloring Album looks like this: If you look carefully at the two images, you'll see that Frank is indeed correct: the dungeons are very similar to one another but not quite identical. Even so, many of the most iconic features of the Holmes dungeon are still present in the Coloring Album version, like the sea caves at the bottom left and the rat warrens at the middle top. Zach Howard, over the excellent blog Zenopus Archives, has a useful post in which he looks at some of the similarities and differences between the two versions.
I'm fairly confident that the map appearing in the 1977 D&D Basic Set was created by Holmes himself, though I'm 100% certain of this fact. If so, that makes its reappearance in the Coloring Album, albeit in modified form, all the more fascinating to me. Why was it chosen? Was it because its compactness made it especially suitable for the pared down "D&D Lite" of the Coloring Album? Why not make an entirely new dungeon map? I suspect the answer is probably fairly mundane, but I can't help but wonder.