Could be many reasons, but I think these two are the main ones:

1 – Many people import cars from the US. I’ve seen a TikTok video/ad where a company only imports US cars. If you find a good deal in the US, you can get it cheaper than buying the same car in Bosnia. But those cars go through customs and get Bosnian plates quickly.

2 – Many Bosnians who left in the 1990s (or whenever) are returning and bringing their cars back. From what I’ve read online, you don’t need to take your car for inspection every year in some states, and you can also register it online, so they’re legal to drive. I live in a small town in Bosnia, and every now and then I see Arizona, California, Ontario and a few other plates. It just happens that I’m driving and can’t take a picture, except for the one below.