FIFA is a game.
The difference is simulator's main focus is reality, games' main focus is fun.
If FIFA was for reality it would be closer to first person QWOP than isometric view of half of field where you have perfect information and you press a key and your player does whatever trick the key was designated to perform.
The substance of the game is lost and only visuals are left.
Soccer seems like it's on the other corner of the "implementation difficulty" matrix from racing.
It's pretty easy to hook up a ffb steering wheel and pedals to a computer, actually simulating the cars and track is the hard bit.
In soccer the actual simulation would be pretty simple - it's an elastic sphere bouncing around a fairly uniform surface and being hit by mostly solid body parts/boots without too many interacting parts. But putting the user into the world in a way that they get the necessary physical feedback is much harder.
MS FS was the engine for some military sims in the early 2000's, and Qantas pilots did IFR currency practice on it when I was flying in NZ.
Although the terrain was pretty good, what made MS FS acceptable for pro use were the excellent instrument panels.
I guess it's not the market leader for a reason
Not that I would consider FIFA a sim, but I have to assume that, like racing, at least some knowledge of the strategy carries over.