Vita was lacking some very useful marketing technology hype when DS, Wii, 3DS and even PS4 all somehow got some at launch.
3DS still brings something with its hardware no other mobile device does.
So do the twin sticks and the rear touchpad. Most people have the 3D slider all the way down. I am one of the biggest 3D fans there are, and the 3DS has some nice uses for it, but really noone seems to care. However, it has Mario. Mario Kart, Zelda, etc - these things do matter. And Vita hasn't kept up in that regard. But Rayman Legends on the Vita is fantastic, so are Zen Pinball, Guacamelee, and a whole bunch of other titles.