Yeah, because they believe (sometimes wrongly) their subordinates read it.
> Understanding of code never existed from the business perspective.
It does, it's called organizational wisdom and domain knowledge, because you need those witty names to sell books to aspiring managers.
>The leader of a product/company does not have to read code.
That's because he's paid a bunch of people 300k to read it and make sure it aligns with the company's objectives and interests. Part of the reason why devs are paid so much is because they're literal business administrators for some narrow slice of the company's operations. The devs are the leaders that you're referring to.
Even in multi-hundred-billion-dollar companies there are so many mission critical things that are owned by just 2 SWEs.