I think the main reason why it has been ignored was because of their horrible (and in most cases, nonexistent) marketing campaign for it.
First they called it the Wii U, which everyone in the entire world recognizes was a bad name for it. Not only is it just an inherently silly name, but it has led to a lot of people confusedly thinking that it's just some kind of Wii add-on. So, the casual family market that Nintendo has always been good at appealing towards hardly even know it exists.

Not only that, but they hardly advertised it at all. At least where I live, anyways. Wii commercials were all over the place back when it came out, and continued to be run years afterwords. I've seen maybe two Wii U commercials on TV this entire time, and it had almost no launch broadcasting at all.

It entered the market so quietly that no one but knows it exists. If Nintendo wants to build relevancy, they NEED to start telling people how awesome the console is, or it will continue to be forgotten besides the much more vocal Xbone and PS4.

Nintendo's marketing department needs to get their shit together.

It really deserves more attention than it has right now.