PS vita is a great machine and people love when they use it. It has games with quality in terms of console but people used to nintendo machines in portables and their IP's. Also 3DS has price advantage and being kids oriented games so every family like to have one, whereas Vita is mostly hardware core gamers machine so it needs more innovations and selling points which its getting with PS4 and more games in future. Vita has bright future with its hardware potential, sony studios and PS4 companion. 3DS can be good for a year or two then its not going to keep up.
The point is Sony not losing money on PS Vita and it just that they are not earning good profits with it right now. So, its no worries for sony and their profits going to increase in furue when more games comes and PS4 support. So, Vita will have atleast 50 million life time and at max close to 80 million.
Its not sales what we should consider about device and its about how much you enjoy. It brings value in many ways with PS+, cross-buy and hardware potential, media capablities etc., Vita is more worth it for the price and has bright future.
GAMING is not about spending hours to pass/waste our time just for fun,
its a Feeling/Experience about a VIRTUAL WORLD we can never be in real, and realizing some of our dreams (also creating new ones).
So, Feel Emotions, Experience Adventure/Action, Challenge Game, Solve puzzles and Have fun.
PlayStation is about all-round "New experiences" using new IP's to provide great diversity for everyone.
Xbox is always about Online and Shooting.
Nintendo is always about Fun games and milking IP's.