Anyone know why ACI doesn't like to do older crashes?

I don't think there's actually anything stopping them from doing it because they have done at least one episode* where IIRC none of those involved in the investigation were still alive. I'm just curious if anyone knows why the aversion to older crashes because there are a lot that would be interesting. Like hell I would love to see an episode on the crash that killed Knute Rockne as that did have actual significant ramification in the industry.

*56 Grand Canyon Mid-Air collision