No, it's not off topic- it seems to fit "history of gaming"
I'll borrow from a comment that @doppelgreener made under the question.
This question is first and foremost trying to understand why a rule exists. It is asking about the designers' own statements secondarily to that; their statements are tangential to the rule's function.
This is the kind of question where both experience and expertise can provide an answer. Granted, I don't think it fits into the "what problem are you trying to solve" category, but it certainly fits into our "History of Gaming" broad category as it establised a precedent for at least one other game system.
Let's face it: there's damned little expertise available (in particular after folks like RSConley, ExTSR and a few others who have been around that long stopped visiting) on this site, for how interrelated the OD&D, AD&D 1e, and BECMI rules are. A veritable Gordian knot to try and unpack unless you were around first hand (at TSR, like ExTSR was) or second hand (as I and a lot of old fart were as we consumed the products as they came out).
I thus offered an answer, though I believe the the 'history of gaming' tag may be the better choice.
Most of what was published in OD&D was never explained. Or, if it was, one had to soak it in as Dragon/Strat Review articles came out. While some restrospective "here's why we did that" is available on places like dragonfoot forums, it's not comprehensive.
As the later OD&D derived systems came out, particularly Gary's Magnum Opus, AD&D (1e), some stuff got a fuller explanation (usually in the DMG) on what was behind it. And some never did.
I'll add to may answer once I dig into a few other blogs among the D&D/RPG archeologists, but the evidence in the AD&D 1e PHB seems to me to explain what was going on when EGG put that terse bonus into the original book: which was tightly constrained by space, and which got ported into BECMI.
What is in BECMI - cited in the question - could easily be explained by @ExTSR, who wrote it, but he stopped feeling welcome here a while back. (Separate topic, and water under the bridge if my last discussion with mxy on that topic is any indication).