Well, its basically, you look at two low selling devices, the Vita and the wiiU... The wiiU has to compete with the ps4/x1 and its getting beat quite hard. Its sales have been piss poor, there is virtually no third party support and it will most likely be in third place by the end of the generation but that doesn't stop Nintendo from releasing its key games on it and giving the fans a fantastic Nintendo experience that they have been looking for.
You compare that with the Vita, each year, the # of games being released from Sony is going down massively... And on top of that, games like FF Type-0, which many fans wanted for the Vita, is being ported to the ps4 instead... Sony could have easily told SE and maybe paid a bit more to port it to both systems but instead, they are just porting it to the ps4... And not to mention, Sony has basically marketed the vita from this dedicated portable AAA experience to a niche indie ps4 accessory experience as well as many other things...
Granted it has smartphones as its competition but so does the 3ds and you don't see Nintendo backing out... Even before the wiiU became such a flop, Nintendo supported the 3ds like crazy and they are continuing to do so with ssb for 3ds just being released and Pokemon on the horizon. On top of that, they have said that there is a 2d metroid on the way (most likely for the 3ds) and they will continue to release more games in 2015