"Why haven't these games been realized?" ...Because some poor bastard like me is going to have to paint all the artwork for it, that's why =P.
My game idea is below. By reading it, you legally agree not to steal the idea for your own use or sell the idea to a major game development company =P.
Kidding aside, I would like to make a game like this someday. It'd be an MMO Wargame. I was going to call it Supreme Commander, but the sons of guns stole my name! (I kid) Players are evenly divided between a number of nations at the beginning of the game, with new players being added to the least populous nation as they join. At the outset of the game, players use an integrated poll to offer suggestions for the name of their respective nation, and then it is voted on. Popular vote establishes the name of the player nations. Technology begins at the level of archaic, mechanical-driven technology (think WWI-II) and continues over the course of the game's years to evolve past the technological singularity, where the nations develop radically advanced technologies, like time, gravity, and biological control. The players essentially research the technologies, which are based on templates the game designers provide, but the players can modify elements of these blueprints by the popular vote method. For example: Player Einstein the Scientist invents the "Plasma Cannon, Mark I". But it is generally decided that this name is boring, so in that nation, it is decided it should be commonly known as the "Dragonmaw DX". Based on popular feedback, researchers also decide to modify it to have a higher rate of fire, but less damage (item attributes can be moved around via a point buy system, with more techonologically advanced items having a larger pool and thus better stats).
Classes include the aforementioned Researcher, Commanders, and Combatants.
Commanders are essentially proven players that have a lot of victories (wether it be good strategic thinking, pvp skills, etc). They are chosen by popular vote to have Officer power. Commanders are much like guild leaders, in that they can invite other players to join their "Company" and organize units into Platoons. In addition to getting a nice stat boost, they can also execute "tactical options". Essentially, a tactical option is a large glowing indicator, placed over the terrain, that directs nearby players to execute a certain action, and buffs them if they do it. For example, commander "The Major" executes "Blitzkrieg", an all-out assault strategy, which places a large blue arrow pointing directly at the enemy forces over your battlefield. Your forces can see the tactic, while your opponents can not. If the player runs into the tactic's area of effect and rushes across the field, guns blazing, he gains a "strategy buff" and runs faster, while dealing more damage. Commanders also provide different passive bonuses and can develop unique strategies. Essentially, this is established by the "character" the Commander takes on. For example, some Commanders will choose to become an "Air Ace" and would then specialize in aerial combat, increasing the overall power of their flying units, like jets, and gaining tactics unique to aerial combat (do a barrel roll!).
Researchers or Civilians are essentially the backbone of the player economy. They research weapon blueprints, develop new materials to contruct things out of, mine resources, and run the home front. Some players may handle morale. Essentially, these are players that paint "propaganda" or record "radio messages" that are displayed around the player nation's cities and factories. Essentially, players can send in pictures or audio clips that, after the game developer's review, can be put into the game as relics of that player nation's pride. Think Uncle Sam's "I want you!" or wierd governmental ramblings over the megaphones. These player inputs grant passive buffs to all players nearby. Other civilians develop new materials, which are required for new research blueprints, can upgrade armor, etc. Iron, Steel, Kevlar, Teflon, Aircraft Aluminum, Adamantine, Ceramic, and so on. Still other civilians mine ore or produce energy. And the researchers basically put it all together, inventing new weapons and armor. Finally, logistics experts transport the weapons and arms to the nation's military installations. (These guys get ambushed all the time =P).
Finally, you have the combatants. These are the meat and potatoes FPS guys, shooting away on the front lines. They attack other nation's militaries, destroy factories, steal researcher's work, bomb cities, capture workers, and so on. War is fought at sea, in the air, and on land, across any kind of terrain imaginable. Jet fighters dogfight, a column of tanks with infantry support rolls across the wartorn desert into a city, sparking intense, urban guerilla warfare.
May the most glorious digital nation win.