So, to make this clear even for DonFerrari, I am not defending the price.
With this out of the way, the Nintendo Switch already surpassed the install base of the Wii U. Therefore, under the false asumption that every Wii U owner already has a Switch at this point, this game is new to every new customer. Therefore, a price like this can be justified even for a game that is already four years old. Skyrim is 60 as well, remember? How old is Skyrim?
Staying with Skyrim as an example, the age of a game is irrelevant, anyways. What matters is if people are interested in buying it for the asked price or if they are not. Skyrim still sold pretty okay as far as we know and people like to have it on the Switch. Super Mario Bros. is still one of the most sold games on whatever form of Eshop it appears. That's the true magic that happens here. Whether DKCTF has a difference of 10 bucks or not is more or less irrelevant in the big picture.
And if you already have it on the Wii U, there is absolutley no reason to buy it again. You are not the target group, unless you want to play it on the go. Nintendo doesn't expect you to buy it again because it has a higher resolution. A few more pixels don't improve the game, seriously.