Zelensky says 31K Ukrainian soldiers killed since start of war? Compared to an estimated 450K Russian killed/injured?

Zelensky says 31,000 Ukrainian soldiers killed since Russia's full-scale invasion, in rare public statement on casualty figures https://t.co/Z1dtf6OPxd

— BBC Breaking News (@BBCBreaking) February 25, 2024

This makes no sense. How can the numbers be so low.