After the success of the Wii it's not hard to imagine that people thought they would score again. Surely they would not think it would have crashed and burned like it did...else why back it? I don't think anyone could have realised how little the public would care about Nintendo's new gamepad. As well as that, did EA know how much they would sell it for (ie. a lot), or that Nintendo themselves would not support the gamepad properly?
Points 1 and 3 are down to the spec of the console (cost too much because of the spec, and didn't appeal because of the spec itself - a gamepad), which is why I said the spec was a major reason for its failure.
Again...who would buy the Wii U version and not instead buy it for a competitor console, with fleshed out online infrastructure and existing pools of friends? I'll bet some people...but not that many.