The People page is optimised for browsing rich profile data and is therefore limited to displaying up to 10,000 records for performance and usability reasons. If your database contains more than 10,000 people, the counter on this page will remain at 10,000:
To see the total number of people in your database, use the Query Builder, which is designed for reporting and can return the full record count. A simple way to return all people is to create a query starting with People and the filter applied being First Name → Is not empty, as shown below: