Because Brazil isn't and never has been a world power
Agreed
Because Portugal/Netherlands aren't as important historically as Spain/France. Not sure why the Vikings aren't in it, but perhaps because their bonuses would have been too close to a different civs?
Portugal and Netherlands were kind of important, but less so than most of the other civs in the game.
Egypt and Greece are far and away more important than Sumeria, Babylon, or Persia, the only reason I can think for Arabia to be in the game rather tha Babylon or Persia is because Arabia had more technological impact on history than they did.
There's no reason to include all 3 of those civs, but at least Persia should be included, they were very important in history. As for Babylon and Sumeria, they were kind of important, but not important enough to get in the game.
Amazonians were barbarians, not a civilization, and the only reason I can think of to only have the Aztecs and not the Incans and Mayans is because they could only include 16 civs in the retail version and couldn't very well devote 2 out of 16 to American civs.
Agreed on the Amazonians. Also, the Mayans didn't do much of historical impact. The Inca, on the other hand, had an empire spanning most of South America's west coast, which contained about 10,000,000 people. And they managed that empire without a written language.
Because Rome is one of the greatest and most powerful empires ever, and the Byzantines are Roman in origin, while the Celts were not really an empire until after Roman rule.
I agree that the Byzantines and Romans don't both need to be in, even if the Byzantines were important in the middle ages, but the Celts were reasonably important, even before being conquered by Rome.