Accretion

There's another point made in the comments of the theoretical framework post, a point which has also come up in other discussions about the origins of specific rules: many of the rules in the original three books were adapted or even copied directly and completely from other games. The most obvious example is the combat system, which officially was supposed to be Chainmail. No rewrite, not much in the way of modification, and in that case not even a copy or summary; just a suggestion that you use Chainmail to resolve combat, and an alternative combat system in case you didn't have Chainmail. Another example was the suggestion to use Avalon Hill's Outdoor Survival.

Others more familiar with war games and strategy games have done the work I can't, explaining where some of the systems like morale and reaction came from. But the general point is that "D&D is Always Right" because it used stuff that already worked. When someone needed something new, like potion miscibility rules, they adapted techniques they already knew about and shared their work with others, who could then borrow or adapt as they pleased.

This process of accretion sometimes created conflicts in later editions. It's said that no one, except I suppose tournament players, played AD&D 1e the way it was written. This is because it's a big ball of a whole bunch of rules that were available. It was not necessarily what anyone was looking for (except those tournament players.)

I think I had a Big Serious Conclusion based on this observation, but now it escapes me.