They have also filmed in South Korea, and looks like the movie will feature the new electric Harley Davidson

I think its because:
- "film producers don't had any idea about what cars are/were used in the former Jugoslavia", like ElSaxo said;
- the stereotype that is spread all over the world, assuming that almost everything is old and rusty in eastern countries⁽¹⁾, and new things exists only because of the Mob (you'll always see big luxury new cars, not small popular ones).

I think we cannot hope from that kind of movie to work on that kind of cliché
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(1):I don't see any 2005+ car in the pictures. For me, they're not old, 10 to 15 years is the average age of the cars I owned .
But it seems that the producers try to "say" us something with this...

Yes, but they do that due to the lack of recent French cars in US.
Here they are mixed with modern ones, hence why I find that strange.

The same way French locations were depict in not-so-old US tv series by studio scenes of small villages with an old 2CV or R4 van, a Ds and one or two scooters, plus one or two men (and women) wearing a beret (they didn't dare the baguette )...
Some times, there was a Peugeot 505, for a more "recent" touch

In one of the news article, was stated that they filmed the scenes in Aosta, Italy, standing as Novi Grad (it's not stated if in Belgrade or Sarajevo). Evidently film producers don't had any idea about what cars are/were used in the former Jugoslavia and based on stereotypes for the traffic they have taken a mixture of "oldies" and much recent vehicles from what was available there.

Possible, but it is weird to use historic cars mixed with common recent ones...

Perhaps they rented historic cars from local collectors for a few money and acquired old wrecks from local junkyards for even less... I even see a Trabant... (never seen one in Italy)

The explosion between it and the Trevi seems dangerously close to these two... Strange to have these mixed with common newer cheap cars (well, these older ones are cheap too I guess, unfortunately)

Danno un sacco di soldi alla Rai per il solito noiosissimo veglione di fine anno con Carlo Conti, figuriamoci quanti ne avranno dati per i "vendicatori".

By the way, I really think that they got public funds for filming there: http://www.filmcommission.vda.it/pg_gen.php?lang=it&id_cat=3&id_scat=5&id_sscat=- 4&lang=gb.
Also, evidently a film set in Eastern Europe can never lack of a Fiat 131 (wonder what's the station wagon parked next, it's in the vimeo video posted here).

I don't get why film scenes set in eastern country, Russia I guess, in Italy... Usually it's the other way round: since in Italy is more expensive to film movie scenes, they rebuilt the italian set in a eastern country like Bulgaria or Ukraine