I can't see how anyone would go for that over a brand new Switch for $300
Because the Wii U is dead now so all of its valuables are up for the taking. The Switch is like a stubborn old man who may die sometime soon allowing you to take what he has, but for now he hands them out piecemeal.
The only thing TC would miss out on by not buying a Switch right now is Mario Odyssey which isn't coming out for another half year, and probably not worth buying a system for just that one game. The Switch will definitely be better in the long run, but the Wii U a cheaper option with dozens of games to buy, hundreds more with Virtual Console, and no droughts since it's already dead. For us Switch owners, the last two really good games are both TC could still play on a Wii U, and I wouldn't consider ARMS a system seller by any means.
With a Wii U, he pays less to immediately get Smash, Mario Kart, 3D World, Xenoblade 1, Xenoblade X, EVERY Zelda game with the exception of literally 2 or 3 iirc, Bayonetta 2, Pikmin, Wonderful 101, Fatal Frame, all the Virtual console games, etc etc. Versus paying $100 to $150 more for a console that has Zelda and Kart (both of which you can play on the Wii U).
THAT is how someone could go for a Wii U over a Switch makes perfect sense. Switch is a great investment, but the Wii U is the console that has more immediate gratification for less. Especially since a lot of Wii U games are dirt cheap now.