They've learned how to make suckers pay a dollar for a bottle of Dasani and/or Aquafina, which is a much more lucrative market marginwise than soda ever was.
Actually other companies spearheaded the bottled water movement, but Coke was smart enough to see that their success meant soda might not be a cash cow forever and started diversifying. Of course with their marketing and wholesale clout they pretty quickly killed most of the other water competition.