We don’t have a national ID, which is part of the issue. As a result, regular identification is by state depts (motor vehicles).
It also means for passports, you need to either fill out the form and mail it in, or visit a State Dept office for some expedited options (requires specific reasons to do so, requires an appointment).
In recent years, the Postmaster General has royally screwed the post office (that’s a whole separate thing, so I won’t go into that here. Short answer, Trump). So it runs pretty inefficiently, and that’s the main way that people are getting passports.