I don't have time to dig up the story; and surprised it hasn't been mentioned here yet. There's a back story to this whole thing: valuable real estate and donations to the mayor. The real reason for getting rid of the horses has nothing to do with the horses - it has to do with an opportunity for one of the mayor's friends to make a whole lot of money; something to do with the property where the horses are kept.
Edit: found an article. I don't know how valid the article is, but it does give a little food for thought. Of all the issues plaguing NYC, those horses have to be pretty damn low on the list of priorities.
http://www.theblaze.com/stories/201...yc-mayor-vowed-to-ban-horse-carriages-in-nyc/