They don't have control over measurement. Consider also it's easy to figure this out and it creates a scandal. Like I said, consider Llama 4 which a lot of people pointed out used a custom model in LMArena to inflate their scores; its never clear what the true underlying story for this, but regardless that model release spurred billions of dollars of spending on new talent and a complete gutting of that org.

These companies have to care about good measurement frameworks because the quality of their models depends on it. Any PR department can polish a turd, but an army of smart researchers far outside the control of these companies are going to figure it out if they are gaming metrics.