I will be honest in saying country is not the top genre on my iPod but I could answer it from the perspective of a similar genre R&B.
Since radio formats have changed and more stations are playing multi-genre formats to get more listeners- i.e. artists are radio friendly by mixing a little of everything in. Therefore more artists are collaborating to hit the popular genres and the most attention. Not that I know but my guess that the most popular genres are hip-hop and pop. Country mixes nice enough with pop and therefore it's easy to sell that way. The same goes with R&B and both genres. Therefore purists are forced to find niche outlets to listen and until the genre is taken over.
It's a theory but I understand how some country listeners feel- R&B and country are the same in that they are story genres- the artists paint pictures with it character and details. And in this day in age- we've become to ADD to enjoy a nice musical picture.