A case of "lots of things have to work perfectly, or near enough, or a brain drifts into this state". This seems to be very much the case with cancers, essentially unless everything regulates properly, the system would on its own devolve into cancer.
Like a gyroscope which will only spin if balanced, only this gyroscope has 10^LARGE moving parts.
And when you consider the ageing process, you're talking about multiple systems operating at 50%, 75%, 85% effectiveness, all of which interact with one another, so it's inevitable that self-regulating mechanisms start to enter failure cascade.
In terms of interventions, a lot of the time it seems like the best fix is to look at which of the critical systems is most deteriorated, and try and bring that one up. So, for example, diet and exercise can restore a degraded circulatory system by a meaningful amount, but you can be an Ironman triathlete and still develop Alzheimers in your 60s. If we can find reliable ways to do the same for sleep, that will be worthwhile, and likely there are other systems where we might do the same - immune, liver, kidneys and so on.