I've come to accept that they are leaving the WiiU to die. The 3DS seems to be getting better though, they know the score when it comes to the handheld bizz
They're most definitely not leaving the Wii U to die. Most of their internal studios have shifted over to the Wii U, meanwhile 3DS titles seem to be handled by collaborative studios and subsidiaries.
Luigi's Mansion: Dark Moon - Next Level Games + Nintendo
Smash Bros. 3DS - Namco Bandai + Nintendo
Castlevania: Lords of Shadow Mirror of Fate - Mercury Steam + Konami
Ace Attorney 5 - Capcom
Pokemon X and Y - GameFreak + Nintendo
Monster Hunter 4 - Capcom
Lego City Undercover: The Chase Begins - Travelller's Tales + Nintendo
Donkey Kong Country 3DS - Retro? Port, anyway
Shin Megami Tensei 4 - Atlus
Mario & Luigi: Dream Team - AlphaDream + Nintendo
Mario Golf 3DS - Camelot + Nintendo
Nintendo's major internal branches are busy with Mario Kart Wii U, Super Mario Wii U, Monolith with X, Retro with who-knows-what-else, and the Zelda team with Zelda Wii U (and maybe the Wind Waker port).
When it comes to third parties, I think Nintendo's in the unfortunate position of just having to deal with the situation they've got. They're a limited company with finite resources. If third parties stop giving a shit, even if it's Nintendo's fault, Nintendo can't wave a wand and solve everything. They can only make X amount of games at any one time, and have Y amount of partnerships (see: The Wonderful 101 and Bayonetta 2).
With the 3DS, the line-up looks good because it's doing well in Japan. Developers are interested it in now, so Nintendo doesn't really have to do anything. They'll make games as it is (arguably) the portable system of choice.
But I also think it's worth remembering that the 3DS is doing really well in Japan only. Sales are still fairly lukewarm in both the US and Europe and outside of a few spikes due to major titles I don't see them getting much better. Japan might love the 3DS, but the rest of the world doesn't.