FIFA games have always been popular. It's the license that does it for most people; the chance to play as the real teams, with the real players, is (and always has been) an attraction for many gamers.
FIFA International Soccer first appeared back in 1994 (though it wasn't until FIFA 95 that EA adopted the familiar suffix). It was the first football game that offered an isometric view; then top-down/bird's-eye viewpoints were more popular. Two years later, FIFA 96 was the first in the series to feature 3D graphics.
For many years, especially in the early part of the last decade, it was Konami who made the superior football games. The International Superstar Soccer series (later Pro Evolution Soccer) was loved by millions because of its fluid control system and intuitive gameplay. It was the connoisseurs choice, and those who braved the creative names and cryptic teams were rewarded with a superior footballing experience.
That's not to say that the FIFA series was bad; it just lacked the quality of its competitor. EA stuck in there, and with the help of the FIFA licensing agreement, managed to keep the series popular. This was despite some seriously mediocre games along the way, but there was enough quality in there to keep EA in the mix.
Pro Evo's position of superiority wasn't to last forever, and in recent years it has been widely acknowledged that Konami's series has stood still whilst the FIFA games have really kicked on.
In the last four years EA Canada has really upped its game. Before then it just had the honour of being the better seller of the two franchises, but the release of FIFA 2009 saw a reversal of fortunes that remains to this day.
In 2009 the gameplay took some giant steps towards realism, and this authenticity remains the hallmark of the FIFA series. It's not just the accurate player and team names, nor the comprehensive and infinitely replayable manager mode. It's not the fine tuning of the online competitive matchmaking, or even the introduction of 11 vs 11 matches.
All of these elements were gratefully received by gamers, but ultimately they are just trimmings around the core gameplay experience, and over the last four years FIFA has reigned supreme in this department. The player animations are lifelike; the recently added Player Impact Engine only adds to the realism. The passing and movement of your players is getting increasingly intelligent. It has become the definitive interpretation of the beautiful game.
When releasing FIFA 12, EA took a bit of a risk. It was always going to sell well, but the game saw a dramatically revised defensive system. For many it didn't feel natural at first, but once mastered it revealed a much more engaging defensive experience. In older versions of the game, defending previously only required persistent use of the soft tackle button. Now players have a whole range of tactical options to employ as they see fit, and to play the game on the more competitive settings or when venturing online, this new defensive toolkit needs to be deployed in full.
I would argue that FIFA 12 is the worthy recipient of its newly earned title. It represents all that has been good about EA's rise to the top of the pile; it's comprehensive, exciting, responsive, challenging and, most importantly, it's innovative. In recent years EA has stopped making football games by-the-numbers. Instead of aiming for the middle-ground, they now take risks and are constantly evolving their game, trying each year to improve on the formula of the last.
FIFA 12 is best selling sports title of all time because EA have changed the way they make their games; instead of churning out the same thing year after year, now they're constantly trying to push the boundaries and make their game better. For taking that more difficult route EA has been suitably rewarded, and rightly so.