The answer has a lot to do with economics. See, modern games can take upwards of millions of dollars to produce. That money has to come from somewhere. Typically, when people invest money, they want a safe, proven investment. Games that get funded, then, are often based off of tried and true models: Formula games, genre games, rehashes, clones ... you get the idea. People with the cash are naturally reluctant to take any big risks on new ideas.
A few examples should suffice. Below I've listed off nearly a dozen EXCITING, fresh new game concepts on the left hand column. Click on the question mark to the right to see what game publishers would rather spend their money to develop [Shockwave is required]. Simple economics, really. Start clicking while I sob quietly in the corner.
THE CONCEPT:
 IDEA: A dynamic RPG with extensive "Game-mastering" AI that will generate unique quests for the player based on the player's actions and behavior in the ever-changing world |
THE REALITY:
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THE CONCEPT:
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THE REALITY:
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THE CONCEPT:
 IDEA: A first-person shooter where the player is forced to choose sides in a Central American civil war. His or her decisions and performance during each mission will change the political landscape and create new missions to choose from. |
THE REALITY:
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THE CONCEPT:
 IDEA: A unique top-down multiplayer RPG with extensive real-time strategy elements where players not only develop characters, but build up armies and construct fortifications on a dynamic game map. Castle assaults and sieges happen round the clock |
THE REALITY:
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THE CONCEPT:
 IDEA: A 70s cop drama adventure game. As a cop who doesn't follow the rules, you unravel a mystery with open-ended Grand-Theft-Auto-style carchases and gunfights at every turn |
THE REALITY:
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