Because Wii U is more in the power range of 360/PS3 as opposed to Durango/Orbis they will lack the ports seen on those systems. The software droughts and lack of diversity on both 3DS and Wii U show this. If they were to continue with two systems, that needed to be their route unless they had something else compelling enough to sell Wii U. As it stands, a tablet controller isn't it.
A console/portable hybrid could have happened if they wanted to. Of all companies, Nintendo was in the best position to do this considering they are not going for a high end console. After doing some research on ARM processors, Nintendo could have gone with their bigLITTLE approach and gone with an architecture that was compatible for both handheld and console. This would put all Nintendo games on one console and alleviate the first party software droughts. For third party support, they could continue the approach they've been taking with Japanese devs. For western support, they would have to target indie devs.