Discussed briefly upthread, but they're for people who entered Schengen without registering in EES, likely because their point of entry wasn't operating EES last time they entered. Given it's a gradual roll-out to every location, and the EU permits countries to suspend EES if queues are building up, there are presumably thousands of people entering Schengen every day without registering on EES. But then their exit dates are still supposed to be recorded in EES (if they leave through a port where EES is operational), hence the need to register on departure.

Obviously doesn't comply with the GDPR principle of data minimisation (GDPR Art 5.1(c)), but we can't expect the EU to start following their own regulations now, can we...? 🙄