The Draconia Kingdom was near the Vogrum Kingdom. Although not that near, it was still the nearest among the rest of the kingdoms.
The Draconia Kingdom was situated at mountain ranges with several volcanoes. Most of the dragons were fire dragons so they mostly lived in places with extreme temperatures.
Although not all dragons were of the fire element, most of them were so the Draconia Kingdom was situated near volcanoes. Dragons of different elements also established cities outside the Draconia Kingdom but were still affiliated with the Draconia Kingdom.
The Dragon King was the first king of the Draconia Kingdom and his reign has continued to this day. After all, the only way to become the next Dragon King was to defeat the current Dragon King.
Since no dragon could defeat the Dragon King, the Dragon King wasn't replaced from his position.