Indeed. What games the Vita gets these days are pretty much visual novels, obscure low-budget JRPGs, and PS3/PS4 ports because the porting process is easy and the Vita's audience has an insane software attach rate.
Developers don't make Wii U ports because they don't want to invest a considerable amount of time and money making special Wii U ports for an audience that, comparatively speaking, doesn't buy 3rd party games. Yes, there are exceptions like Skylanders, but for the most part Nintendo consoles are where non-Nintendo games go to die. Nintendo ports simply aren't worth the hassle, and 3rd party games sell so well elsewhere that they save money skipping Nintendo. Nintendo needs the 3rd Parties, but the 3rd Parties don't need Nintendo anymore. Hardware capability does play a role in deciding software platforms, but ease of porting more so and the Wii U is just too different and too weak for it to be worth the effort. Maybe NX will fare better, so long as it isn't once AGAIN too different to make porting worthwhile.