if we have more users, that improves the value and quality of the fediverse overall

I don’t consider this a given. E.g. your new users might all be dingleberries, or they might attract more bots. It also depends on your definition of quality. I quite like recognizing and conversing with regulars that I know from lemmy. This is something you lose with a larger userbase.

Here’s another way a high monthly active user count doesn’t necessarily lead to a quality platform. Suppose most users post once a month. Conversations will largely be dominated by posts from folks who have no real connection with each other. Any meaningful conversation is drowned in an ocean of seagulls going “have my updoot, kind sir” and “this!”. Higher user count, lower quality.

Aside from that, vanity metrics like bare user count typically don’t tell you whether you have a sustainable non-ad based platform. You don’t need users, you need users willing to donate for the operation (to instance admins) and maintenance (to the devs) of the platform. And I feel (0 data to back this up) like users are more likely to be donating users if they feel like they know the operators and devs personally.

I’m not saying the idea of getting more users is bad, I’m just saying its goodness is very far from established.