>>Just a bit of a puzzle, why would it be in the plurals. Balkan is a single peninsula, named after one single mountain, not a mountain chain.
>
>I thought the Balkan Peninsula got it's name from the tallest mountain, and that the Balkan region (the Balkans) is named for the Balkan Mountains which is a range.

But the peninsula and the region are the same thing, IMO. Which is why the plural is puzzling.

Probably a habit, then - it's singular in South Slavic languages. Funny though that I've seen it in plural a thousand times and it didn't strike me as odd or even weird.

Must be one of those jamais vu moments.