I see that you're using the past tense there. "But what have they done for me lately?" L9 isn't a sinecure. It is a very highly compensated position, and the ongoing production from all of that compensation needs to be high.
But I think you missed the larger point, which is that, during a layoff, even good employees let go. When you let go X% of your workforce, that means you're letting go even good employees. And you're letting go roughly X% of people at all levels. Some L9s were gonna have to go, same as some L4s were gonna go. No one is immune from a layoff. Indeed having people that are immune is legally problematic.
When you do a layoff, you are accepting that you are potentially going to be letting anyone and everyone go. Yes, even high level long-tenured engineers.