So the "multiply by 12" thing is a slight corruption of ARR, which should be based on recurring revenue (i.e. subscriptions). Subscriptions are harder to game by e.g. channel-stuffing and should be much more stable than non-recurring revenue.

To steelman the original concept, annual revenue isn't a great measure for a young fast-growing company since you are averaging all the months of the last year, many of which aren't indicative of the trajectory of the company. E.g. if a company only had revenue the last 3 months, annual revenue is a bad measure. So you use MRR to get a better notion of instantaneous revenue, but you need to annualize it to make it a useful comparison (e.g. to compute a P/E ratio), so you use ARR.

Private investors will of course demand more detailed numbers like churn and an exact breakdown of "recurring" revenue. The real issue is that these aren't public companies, and so they have no obligation to report anything to the public, and their PR team carefully selects a couple nice sounding numbers.