> Apparently it is bureaucracy without purpose after all?

No it's not without purpose at all. The purpose is to know who could be drafted in a timely manner should the need arise. There's currently 2 major wars - sorry "special military operations" - happening, one of which in Europe.

A certain government involved in one of these simultaneously calls for allies to assist while at the same time openly questioning half a century of military alliances. So maybe this helps to understand why regulations like this make sense - even for people who never lived through a time when there was mandatory military service and take their own security for granted.