> I live in Belgium where we already have eID and SSO apps that work okish. But I fail to see the need for an EU wide ID. I don't think most EU citizens use services from other EU countries than the one they live in. Not services where they need to ID themselves. How much of the population would be in the category needing something like this?

Is there reason why this isn't used because noone needs it or because it's too inconvenient to use because we don't have such a system?

EU also didn't do a lot of commerce cross-borders until Schengen, Euro and other agreements made such commerce significantly easier and more viable.