I suspect you have the reason correct. My setup made it very easy for barb camps to go unmolested and hard for civs to expand. The Primordial map I got is very snaky, lots of islands and interminable cliffls, great for canals and chokepoints sort of thing. So late medieval lots of empty land but I can't find barbs only CS everywhere with white borders. Someone suggested Terra Map which I suspect now would lead to this sort of thing as well. Basically to keep barbs in the late game you'd need a world where the Civ can fill up the land before all the camps mature yet still leave some space somehow where barbs can spawn and reguilarly get cleared out? I think I'll still use this mode most of the time but make exceptions for water maps. Those are fun for finding nice settling spots late game and I'd rather clear a traditional camp than annex a CS. It will depend on who I'm playing of course. The meat of this mode is to make those early game struggles with the barbs more engaging without making them too easy.