I wasn't nearly senior enough to have any influence in something like that, but in the internal culture, MAU was seen as such a strong proxy for success that suggesting the metric was flawed would have been sacrilege. The company had big parties and put out press releases every time a multiple of 1 million MAU was hit. To point out that most of those users were bots abusing our service's free tier would be noticing the emperor had no clothes on.