Quote Originally Posted by Kenneth View Post
I found a post on Autosport forum that cites 2002 International Sporting Code: "All drivers, irrespective of the nationality of their licence,
participating in any FIA World Championship event, shall retain
the nationality of their passport on all official documents and in all
meetings and information bulletins."

So it's at least since 2002, but probably much, much sooner. The reason may be decision of some association that FIA is a member of, but it's really hard to find some sources about that.
If I correctly remember, it was because some formula 1 driver had some issues with his own ASN and was forced to use different licence from different country. As they didnt want to have french driver with singapore flag (it is only example, I dont know real countries), they have changed the regulation.