Comment by Earw0rm

And as with a lot of cancers, it seems to be perturbation of a dynamic system rather than a single, mechanistic cause.

Think of it like brushfire in an ecosystem, or species population imbalances leading to catastrophic breakdown. These are better understood in terms of system state and preconditions, as opposed to a trigger event.

Infectious disease, at least in the classic acute form (whether that's bacterial and fast - cholera - or viral and slow - HIV), is a more mechanistic process which can be halted by blocking a single step in its pathway.

Systems that remain healthy and balanced via dynamic processes are harder to reason about and fix, because the root cause of a disease state can be dozens of little things adding up to the system losing its ability to maintain homeostasis.