Because they are treated very different. They are part of the unique political party that runs the company, like in China. Democracy exists only outside the company, inside the company it's the same political system as in China. What that means is that loyalty is the only thing that matters for those roles. Productivity not at all.

For non-Americans: IC = Independent contributor = employee without people reporting to them

I have but it's rarely done by buyouts or with same IC mass layoffs. There is also generally less managers.

Most of time, it's after all IC, they look at what's left, decide what moves to make and lay off the managers.

However, I have seen more and more where managers are told what's happening and they find new jobs before layoffs.

The same reason you’ve never seen the US Congress meaningfully change anything about their role, compensation, etc.