There may be good reasons for it, but they are not obvious to an external viewer.
But isn't the real question whether that obviousness is more important than ease of comprehension and maintenance for someone who does have the required skills to work on the code?
To a child who has just learned squares and square roots and who has never encountered TeX, the expression $e^{i\theta}=\cos\theta+i\sin\theta$ is probably just line noise. To a practising mathematician, it is immediately recognisable and a useful tool. Obviously the difference is that the experienced mathematician has learned the underlying concepts and the notation to represent them. The result is that while the teenager might be learning double-angle formulae by rote for their trigonometry exam in a few years, the experienced mathematician could use their more powerful tool to derive those formulae or any variations on the theme in moments whenever they need them. Their greater skill and understanding makes them much more capable.
There are certainly reasonable arguments for making the code for some projects accessible to new developers, but doing that isn't free if it also means compromising some aspect of that code for current developers. It's a trade-off, and sometimes requiring new developers to have a certain level of skill and understanding before they can work on a project is OK.
But isn't the real question whether that obviousness is more important than ease of comprehension and maintenance for someone who does have the required skills to work on the code?
To a child who has just learned squares and square roots and who has never encountered TeX, the expression $e^{i\theta}=\cos\theta+i\sin\theta$ is probably just line noise. To a practising mathematician, it is immediately recognisable and a useful tool. Obviously the difference is that the experienced mathematician has learned the underlying concepts and the notation to represent them. The result is that while the teenager might be learning double-angle formulae by rote for their trigonometry exam in a few years, the experienced mathematician could use their more powerful tool to derive those formulae or any variations on the theme in moments whenever they need them. Their greater skill and understanding makes them much more capable.
There are certainly reasonable arguments for making the code for some projects accessible to new developers, but doing that isn't free if it also means compromising some aspect of that code for current developers. It's a trade-off, and sometimes requiring new developers to have a certain level of skill and understanding before they can work on a project is OK.