Don't know who, but somebody in power in the EU considers all three wheelers motorbikes. Anyone who passed their car test after 19th January 2013 and is not yet 21 cannot drive one thanks to the third EU directive on driving licences. And even when they are 21, they cannot drive one abroad.
A full motorbike licence is the only current legal way of getting an exportable licence. Older car licence holders are grandfathered.
Largely admitted to be lunacy by UK officialdom and the pressure is being maintained for the fourth driving licence directive (when it comes) to put some common sense back in.