It was widely speculated all season that CBS was going to cancel one of the 'CSI' spinoffs, either Miami or NY. Even though the ratings were better than most on the CBS schedule, it still wasn't enough because the cost of production out-weighed the ratings.
Here is the break down of the last five aired episodes:
Episode 15 - No Good Deed - March 4 - 10.14 million viewers
Episode 16 - Rest in Pieces - March 11 - 10.72 million viewers
Episode 17 - At Risk - March 18 - 8.54 million viewers
Episode 18 - Law and Disorder (Part 1) - March 25 - 9.29 million viewers
Episode 19 - Habeas Corpse (Part 2) (Series Finale) - April 8 - 7.94 million viewers