Why did Romans recruit so many Emperors and soldiers from the Western Balkans, in particular the Roman province of Illyria?

Posted by Chance-Struggle-6285@reddit | AskBalkans | View on Reddit | 77 comments

Been watching a video of Ranked Roman Provinces, and out of all of them Illyria ranked first due to it being a recruitment ground for soldiers, but also the amount of Emperors that originate from that region. What is it about Balkan people that made Rome, or even Ottomans recruit a bunch of soldiers from (Devşirme system)?