Explanation
Organic reach has no invoice, so it tends to get valued at zero by default. Multiplying organic impressions by the CPM you would have paid for the same reach is the fastest way to make the case for a content budget, and it is a defensible number rather than a rhetorical one.
On short-form specifically, creative moves CPM further than targeting does. A hook that holds attention lowers effective CPM more reliably than most audience adjustments, because the platforms price delivery partly on how well the creative performs.
The common mistake
Reading a low CPM as success. It measures delivery, not results, so a cheap CPM against the wrong audience is an efficiently wasted budget.