Exactly the reason Sphero Pefhany mentioned:
The risk of theft and loss of car is much too high.
The long time of the Cold War lowered the living standard in Eastern Europe, most countries in Eastern Europe have still very cheap living costs. Eastern Europe also joined the EU very late, so the income gap was still very high.
Therefore many organized and high-professional theft gangs exist; most of the cars are stolen in Germany (especially luxury cars), moved as fast as possible over the border and then worked over in workshops (For example: 64 % of all car thefts in Berlin and Brandenburg are committed by Polish gangs).
Some of the thiefs are capable to remove immobilizers, but they sometimes take several cars of the same type apart completely apart and exchange parts to make identication and recovery impossible.
After Eastern Europe joined the EU, the increasing wealth and the higher standard of living caused a steady decrease of thefts, but still the numbers are very high and the new EU members are still a transit land to the other, non-EU countries like Ukraine or Belarus with a high demand for cars.
ADDITION: In the comments it was asked why some brands can be taken over the border. That is easy to answer: It is not sufficient to have a car, you need also the whole infrastructure of spare parts, so you look out for brands which are widespread in Europe, have a high demand and are therefore easy to sell.
No Škoda (Czech), no VOLVO (Swedish).
Honda and Toyota build excellent cars, but they still are in the minority, are conspicous and have more a reputation for reliability than for projecting images (Except the ATVs/jeeps, they are also very much sought-after). Ford is mostly American.
Thiefs also try to maximize the gain, so they specialize in specific brands with high resale value where they know the security measures and how to manipulate/circumvent them. So even a reliable luxury car can be taken over safely if it does not match the target profile of the thiefs.