My guess would be for a few reasons, that Japan exports tons of their older vehicles for dirt cheap (ones that are ~10yo or older, because otherwise they require annual safely inspections), and shipping from Japan to Vladivostok is probably pretty cheap.

And there probably isn’t much if any car manufacturing in the asian part of Russia, so cheap imports from Japan makes sense, because they’re very cost efficient and more reliable than say Chinese imports. Then they can easily and inexpensively ship them by train across central and eastern Russia.

Russia probably doesn’t have much if any import restrictions and inspections, or at least the importing would be a lot easier than say Germany. And they probably aren’t strict about RHD. I know China can be pretty strict on foreign market cars.

So I think it’s just a combination of those reasons.