Sure there are also other factors, we can discuss them too.
If you want to play with actually different factions, would you pick up for it a historical RTS?
Obviously not. Sure you can give it a try, but in the end you would go back to Starcraft or Warcraft, that are not only superior, but also very well populated with real people. If other games do try their different factions, caster units, play fast, carton style, it is fast dead online. I just can’t really recall any RTS, that did benefit from it.
The big Problem I have right now with AoE4,
it simply does remind me a lot of AoE Online.
Do we really need another AoE game to fail?
I just don’t see why people would pick up right now AoE4. As mentioned here by DivineBoon, Total War 3 Kingdoms, was bought a lot because it did have china. And he is right, people would rather buy a game that does represent their culture, history and nation.
In case of AoE Online Greek and Egyptian do still exist, but Celtic, Persian, Babylonian, Norse are kind of no longer around. That’s why having a handful of nations might be not enough. It also have to be the right Nations. Britain did not fight Mongols. And Mongolia is today a very small country, with just 3 million people.