The reason there are only 2 right now is pretty straight forward. The FAA and most flying schools included were under the impression that the airlines would roll the new ATP requirements into the training of new hires. How many schools that used to do ATP flight tests have full flight sims on site? We'll Embry Riddle and ATP are the only ones it seems due to their strong ties to regional airlines in the US.
More will come. I'm sure the likes of Pan Am and other training providers will follow suit. This will hopefully bring the price down a bit too.