Nintendo, in their infinite wisdom, hasn't reprinted it and the original print run is now all but sold out.
It was a lengthy journey to selling out as Nintendo doesn't typically follow the usual practice of dropping prices to maximize sales, meaning that inventory had to trickle out at or near launch MSRP after the initial release when it saw most of it sales. But over the past six months, prices have steadily been on the rise as that supply finally dwindled.
And the icing on the cake is that Nintendo just recently released a demo of it on the eShop. While available in full on the eShop meaning that there was a purpose behind it, why they didn't lower the price and reprint this fine release at retail at the same time is anyone's guess. The Wii U is a troubled platform, this is a fine game that has sold about all it ever will at original MSRP, and could've sold many more copies at a lower price. And it's in a franchise that they're clearly invested in and would like to grow.
Yet it's essentially only available via the eShop proper, where apparently it's still $59.99 according to at least one major retailer that sells the download code (I didn't fire up my Wii U and check). Just another example of their foolishness that so often puzzles everyone else.