Another very common reason is to create a predictive model without caring about actual causation. If you can't do interventions but would like to forecast the future, that's all you need.
You'd also like a guarantee that others can't do interventions, or else your measure could be gamed. (But if there's an actual causal relationship, then 'gaming' isn't really possible.)
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.
Notes for future OT posters:
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