In Nintendo terms there aren't very many people willing to buy their console as is, the portables are overwhemingly more popular and if the portable can now play all the same games ... I dunno.
I think there is a controller gimmick or some kind of novelty at the core of this design too, so perhaps it being something that can be moved easily around the house is part of that. Nintendo may have recoginized that just releasing another portable wasn't enough in light of smartphones/tablets, they need something else that makes it stand out, other than just "well you can also play these games on your TV". That's a decent feature, don't get me wrong, but it's not "OMG! I have to run to the store and buy this now" type thing.
U completely ignored what I said. We have no idea if Nintendo handhelds are more popular simply because they are handhelds or if it's due to other factors like price or game selection.
If 3DS & Wii U launched around the same time, at the same price and with all the same games than its very likely sales wouldn't be in such a huge favor for 3DS. Instead of outselling Wii U by over 5:1, it may be more like 2:1 or 3:1.
That's something Nintendo needs to try before completely cutting off one side of their hardware. If NX Console sells 30 million & NX Portable sells 70 million than keeping around a console variant would definitely be worthwhile.
When the herd loses its way, the shepard must kill the bull that leads them astray.