Ask HN: How do opensource projects know who is using their software?

I've noticed many opensource projects publish who's using their software on their website. Typically it will be big name enterprise and trendy startups. What different methods they use to find that info out?

For instance https://nextjs.org or https://www.styled-components.com have big names on their websites, but neither seems to track who's downloading their software.

I also wonder if they ask for permission before putting that information up. Depending on the software/user, it could be sensitive information that may require explicit approval.