Have you even read the complete list of what BTS is going to bring? I can tell you that, though I like new Civs, it is not what I am most excited about.
* Expanded Epic Game: We've added more new units, buildings, and technologies to the epic game with a tremendous amount of effort focused on the late game.
* New Game Scenarios: The expansion will deliver 12 new scenarios custom designed by the team at Firaxis and some members of the Civ Fan Community.
* Corporations: A new gameplay feature similar to religion that allows players to found companies and spread them throughout the world. Each corporation provides benefits in exchange for certain resources.
* Espionage: Now available earlier in the game, this feature offers players many new ways to spy on opponents. Each civilization has the opportunity to fund espionage development, which will allow them to gain intelligence, sabotage structures, poison water supplies, cause rebellions, and much more.
* Events: New random events challenge players with unique ways of interacting with the world. Players are presented with interesting decisions to make when faced with events such as natural disasters, pleas for help, or demands from their citizens.
* New Wonders: There will be five new wonders including the Statue of Zeus, Cristo Redentor, Shwedagon Paya, the Mausoleum of Maussollos, and the Moai Statues.
* Expanded Space Victory: Winning a space ship victory will now require more strategic planning and tactical decision making.
* Apostolic Palace: The United Nations will become available earlier in the game providing a way for players to win a diplomatic victory earlier. New resolutions will also be added which will expand the available diplomatic options.
* Advanced Starts: A major fan request, this new feature will enable players to "buy" components of a custom-tailored empire and begin play in the later part of the game, allowing them to experience many of the new features of the expansion in a shorter amount of time.
* Enhanced AI: The AI has received many enhancements making it tougher to beat on the higher difficulty levels. The ways in which the AI will attempt to achieve victory have also been expanded.
Tossing in new Civs and leaders is the easiest thing for Firaxis to do and I *guarantee* you that every single one of the above mentioned additions took far more effort to complete.
So what's the complaint here?
We're getting natural disasters, new units, new buildings, new wonders, enhanced espionage (poison water supply, come on!), corporations... I mean, it's even quite possible that "Events" could include such things as civil war!
And if that's not all, they spent their focus on what is the deadest part of the game: the gunpowder age and beyond. Everyone knows that the early years are where the fun is at and that the meta game is slow and drawn-out. They're enhancing that with a ton of new crap that'll up the ante and make it as fun as the earlier ages.
What more do you want from them, exactly? Everything that I mentioned above modifies and adds to the gameplay, keeping the game fresh.
I mean... I really don't see how you could possibly think that new Civs and leaders is Firaxis's focus when there is so much on that list.
As for new Civs and leaders, it's simple: people like variety. Official variety. Mods are lame and most gamers are purists. Firaxis knows that.
If every single gaming company operated on the "well, the fans have already made a mod for that, so I guess we won't bother to make an official version of that great idea" philosophy, then we'd be seeing some reaaaaaally crappy development.
Companies can't and shouldn't rely on the community to make their additions for them. Which is why they make official versions of the mods, that's how the industry works. It benefits them and the purists, who are the majority of their playerbase.