The world can feel very small and empty with only 10 players (ai or human) per game. If you split players between a couple continents, you'll just share your continent with a few other players, limiting the combinations of alliances, wars, back and forth competition, and general variety of challenges and decisions. If you put everyone on one continent, it helps a bit with those issues but then you quickly meet everyone in the whole world and then there's little fear of the unknown or hopes for discovery or new challenges appearing later in the game (by meeting a new superpower for example or a new continent with all its own history, alliances, complexity). 


On bigger maps the low player count also usually means that the first couple eras are just about expansion into empty territories, rather than any meaningful conflict with a neighboring nation. So little chance of reliving the unification of ancient Egypt or Akkadian expansion. It also means that you only realistically have a couple competitors to worry about, then once you win a war against them or progress faster than just those couple leaders you're kind of done, which can happen by mid-game if you play the longer game speeds. In my thinking, there have very rarely been times in history where a civilization could expand somewhere uncontested, and up until relatively modern times there were always more civilizations to meet. I think it would be really nice (i.e. more challenges, more variety, more decisions for the player to make) to have multiple layers of neighbors that you're meeting, befriending, or conquering throughout the course of the game.


I propose that there is no hard cap to the number of players, and have an option to allow cultures to repeat. There should be a soft cap and warnings about performance of course. But if someone wants to have 20 Greek nations and relive the Peloponnesian wars, take advantage of their high-end PC (or not mind longer turn times) and have a few dozen nations challenge each other through the course of history, or feel like they can truly have long, epic games where they are meeting challenge after challenge, then why not? Then through DLC and modding as more cultures get added, the options for reliving any moment in history or for creating your very own stories are (almost literally) limitless.