Most of these questions are about identities that have sometimes been discriminated against (intentionally or unintentionally). The reason for asking is to make sure that the process is reaching the people it's supposed to. Like, if you're running a vaccine clinic that is intended for everyone, but women don't feel comfortable going there, you'd like know that's happening so you can dig into why.

As people have mentioned, this applies to hiring -- but at the top of the funnel in who your posts are reaching/motivating, not just at the end for diversity stats.