Lore exists: (I feel guilty for copying and pasting from RS Wikia, but they sum it up)
The lands are noted by "western" explorers to contain many exotic items and people. Ak-Haranu, Necrovarus, San Fan, and Shanomi are known to come from there.
According to Trang and Mauritzio, the Eastern Lands are also home to the endangered black rhino and white rhino. In the real world, these animals are native to Africa and are also endangered.
It's possible they just copy/paste everything from OSRS's Zeah when it is done.
The Wushanko Isles were a known location, but was cut off for 20 years because of the rise of sea monsters.
Given the average life expectancy of an NPC in game, we've probably slaughtered everyone/anything else with a combat level that had knowledge of it.
So who knows what reason there was for cutting it off.
They might even go beyond the 4th wall saying that they cast a spell that made them seem like "nothing" (a reference to the old black spaces that used to cover unused areas of the RS map), so while they were still there and lived their lives, no one from the Western Lands or even the Wushanko Isles could do anything for a long long time.
11-Oct-2016 23:15:03