It's true that keeping track of how many models are out there gives us some numbers, but that doesn't make tracking the primary reason for growth itself.
This whole idea that observation equals causation is a common failure mode when people talk about tech.
The tracking mechanism is just counting; it's like saying the thermometer makes the weather change.
The weakest link in this claim is ignoring the actual developers and market forces, which truly drive how many models are available, for example, if a company decides to pull their model from OpenRouter, the number goes down regardless of any tracking efforts.