> only a concern if you're charging money

No, it's a concern if you care about impact. Improving commercial profits is one kind of impact that is relevant to for-profit corporations, but there is also impact like "improving user privacy" or "helping lower-income people manage their finances with a free-as-in-beer product". This impact can be measured and the feedback can be used to improve the product according to non-profit, non-commercial goals.

There are also people who build open-source software as a hobby and couldn't give two shits whether other people use it or not. More power to them. For those people, you are correct. https://book.iced.rs/philosophy.html comes to mind.

Then there are projects like Streisand (maybe a bad example, I see it has since been archived, but it came to mind) that want to change the world in some way. Those projects very much do need to care about metrics like, how many people are downloading the software, are people opening GitHub issues, are we obscure or is our target audience talking about us, hopefully positively but if not, how can we improve that? Value must always be worth the cost (even when the code is free, it must be worth the time to download, give it a try, give it CPU/RAM, maintain/upgrade the installation) - are we giving users value or are they churning?

It might blow your mind but even non-profits hire people with MBAs (and universities offer programs for MBAs that focus on non-profit management), precisely because some organizations focus on non-financial impact.