Word on the street is that Tetris will be removed from eShop when 2015 arrives. Not only that, but previous version of the game Tetris Axis will also be removed from retail.
Since I'm not a real journalist and lack the proper investigating skills I am unsure but would put my money on this having something to do with the recent Ubisoft Tetris game arriving in stores.
So go grab the game ASAP, it's something nice to have on 3DS to
waste spend some quality time and remember those simpler days. And now that you're properly warned, some shameless self promotion.