There's a few reasons I think it wasn't the commercial success it could have been.
1) Memory cards. Not only are they proprietary, meaning you can't get a third party one if you wanted, but they also ridiculously expensive. You could get maybe 2-3 retail games for the price of the 32GB card in stores. Also, Sony never released the 64GB in the west, which is a problem for someone like me who buys a lot of games (especially with the flash sales and buying more digitally). I think a better price point for memory cards would've been $50/$65 or so for the 32/64GB one.
2) When the Vita released, they had the 3G model, which probably didn't profit too much when compared to the cheaper Wi-fi model. Plus, it might've been a bit too expensive, although I'm sure Sony was taking losses with the Vita at first. When they saw that the 3DS wasn't selling at $250, I don't think they should've debuted at that price either.
3) Marketing/Games. They tried to sell the Vita as console gaming on the go, but after the first big batch of games, companies saw that those kinds of games weren't selling, so they stopped making them. Fast forward to now and the system is primarily for niche and indie games. I also feel that Sony abandoned the system itself in regards to game development, which is a shame, since Killzone, Gravity Rush and the Uncharted for it were all great games.
Also, where was the advertising for the system? There was barely any TV ads for the Vita and they also lacked presence for it at shows like E3. When people saw that Sony wasn't pushing the system, they thought to themselves that it was abandoned and didn't buy it.
