Holger, I thought you were from Eastern Europe. Perhaps I remember wrong.
I would attribute it to (this is a layman talking, not an expert)

Fuel costs about 3-4 times our prices, so small differences magnify.

Small, fuel efficient diesel engines in small, light cars....that spew pollution at levels not allowed in the USA. (But less cars on the road and less average driving per person; they don't have the pollution problem we do. Amazingly, we're going to have much cleaner diesel than the environmentally conscious Europeans).

Diesel was cheaper than gasoline (probably because refineries were geared to produce it more than gas)

Diesel engines get better fuel efficiency. (See that part about fuel costs again)

Every gas station I ever stopped at from Britain to Northern Germany, to South of France, to the Croatia and many of the "oknias" and "stans" has diesel, so there's a continent-wide infastructure, unlike the USA. No fear of getting stuck in a small town way off the highway.

Again, just a layman. I like diesel and wish we had the option.