I think you might be confusing cause and effect here. There used to be a lot more choice in all sports games but EA has almost completely taken over sports gaming in the last few years. To my knowledge, we now have the following very limited choices for sports gaming:
NHL - EA only, used to have 2k and Radical's Powerplay series in the past
NFL - EA's Madden, used to have Front Page Sports Football and 2k
MLB - 2K/Sony, I miss High Heat baseball from the past.
NBA - 2k/EA coming soon, the same as it has been for quite a while
Soccer - EA/PES, used to have a lot of different soccer series
It is worth noting that all of these are available on PC except EA's NHL/NFL games in which they have a monopoly on the sport and of course Sony's The Show series which they want to keep console exclusive. On PC, people can make mods and extend their game experience for years, look at what people have done with NHL on PC and what they are now doing with FIFA 13 on PC. EA hates this and I think that is why they stopped making games on PC where they can get away with it and people have no option. They make all games on PC in categories where they actually have to compete with others.