Why was it Cancelled?

It was probably a financial decision, a common factor in cancellations. For most of its run, CSI: NY had (at least on average) 24 episodes a season. However, seasons 7, 8, and 9 had 22, 18, and 17 episodes, respectively. In retrospect, it was not a good sign.

Some of the promising shows that got high scores from viewers were not picked up only 6 episodes into the year cancelled. What gives???

Viewer praises don't guarantee high viewership. When a show is canceled after airing only a few episodes, it is because the Nielsen ratings were too low. Unfortunately, networks are impatient and very quick on the trigger to cancel a show as soon as its Nielsen performance is not to their satisfaction. Of course, it wasn't always this way. Take a look at Seinfeld, X-Files, Cheers, and The Dick Van Dyke Show (just to name a few). They all initially struggled find an audience, but after a while more people tuned in and they all became long-running hits.

I loved this show still watch it on nextflix. I hate it was canceled and left us with lots of unanswered question.

I agree with you CSI:NY is such a great show, it's so disappointing that they cancelled it.
As for NCIS well...I was a big fan of that show in the beginning, but it has since gone downhill in the past several seasons and has become less interesting to me, I don't like it as much as I did in the past. And the show is not everyone's cup of tea that's true, you either like it or not, especially with Abby's character I think, you either like her or dislike her.

I have to admit, I am more hooked on CSI:NY than I ever was with NCIS, even though I was such a fan of NCIS in the past, so it really disappoints me that this show has been cancelled while NCIS is still airing. But let's face it, NCIS have always had better TV ratings than this show, and networks will always look at the ratings. Ratings don't necessarily mean quality, but it's certainly crucial and the most important factor that networks look at when they determine which shows stays on and which ones get cancelled, sadly that's just how things works. Then again if you think about it, the people we should blame are the viewers, the choice of shows that the general public likes to watch. And the fact is that NCIS tends to attract more viewers than CSI:NY ever did, and that's not CBS' fault, it's not their fault that so many more people like NCIS more.

I don't know why CBS cancelled CSI:NY, but I think ratings was at least one of the main reasons if not THE main reason, the ratings for the show dropped significantly ever since Melinda Kanakaredes left the show. There's some speculation that season 8 was suppose to be the last, due to the fact that it only had 18 episodes and the finale seemed alot like a send off. But then CBS renewed it for a 9th season with only 17 eps before they officially cancelled it...I think the higher ups at CBS weren't sure what to do with the show in the end, so they played it "safe" with the last 2 seasons by cutting the seasons shorter and wrapping each finale up like a send off in case it doesn't get renewed.
I heard CBS fired Melinda after season 6 to save on costs...now I wonder if that was the right move on CBS' part, her character Stella was such a popular character on the show and the show lost quite alot of viewership after she left, and the opinions about her replacement Jo/Sela Ward have been largely mixed with viewers. I wonder if the show could've lasted longer or if it would still be airing now if Melinda/Stella never left. I liked Jo, but I have to admit that I still prefer Stella and would've wanted her to stay on the show till the very end. If they wanted to cut down on costs, then just make the seasons shorter and keep Melinda on the show.
With that said, I think CSI:NY still could've lasted a couple more seasons or at least 1 more season though...there are other shows that get roughly the same kind of ratings as this show did for the last 3 seasons and they're still airing. Furthermore, the ratings for season 9 in general actually improved slightly compared to seasons 7 & 8 (but I think that was partially because CBS cancelled CSI:Miami). So if CBS had renewed CSI:NY for at least 1 more season, it's possible the ratings could've continued to improve.