Normally, one uses advanced carpentry techniques to look nice, or to make it strong and light. None of those are a restriction at the bottom of a well - Why not just use a thicker bit of wood and a basic unpinned miter joint held in place by soil?
When you're carving wood by hand, why go to the extra effort of fancy complex joints for no gain?
A well back then may have been quite a proud and precious thing you point your best builders at, considering it was the life source for the area village/farms.
Because a bunch of complex joints are likely less labor intensive than using larger material. Remember, these "planks" were made by hand. It's the difference between spending an afternoon shoveling dirt or spending an afternoon fixing a tractor to shovel the same amount of dirt in 5min.
This gets conveyed as "here is how you make a strong joint". The knowledge of "strong enough", or "this thickness and a miter joint" is stronger than a "thinner joint but with a tenon" implies a rigor in the way knowledge would have been passed on and organized that we know largely didn't exist.
This sort of thinking and understanding is often apparent in medicine practiced in primitive tribes. There generally isn't a systemized, unified theory or understanding of dosages etc. in medicine but instead "scraps" of knowledge and facts.
In short, I wouldn't expect that a builder sat down and said "here are my four joints, which should I use" when constructing this, but instead said "I know a mortise and tenon is the strongest joint so we will use that" because the analysis of "is it strong enough" both wasn't practical and wasn't understood.
The knowledge of "strong enough" is something that anyone building without a desk reference on safety margins and the material wealth to build to those margins will learn to understand very well. You don't need a system to pass down that kind of knowledge because everyone will live their lives around it.
>In short, I wouldn't expect that a builder sat down and said "here are my four joints, which should I use" when constructing this, but instead said "I know a mortise and tenon is the strongest joint so we will use that" because the analysis of "is it strong enough" both wasn't practical and wasn't understood.
It wasn't consciously understood but whoever built it likely took stock of the situation (task that needed to be accomplished vs available materials and labor) and concluded that how they did it was the best way which is basically a less formal version of what you're describing.