WiiU has a lot of great games you can play right now and it will take Switch few year before it reaches a similar level in it's life cycle. Also, it's the best console to play Wii games right now (and possibly ever) and there's plenty of games available from Nintendo's older consoles available on eShop. Considering that in few months it will be nearly impossible to buy a new WiiU I'd say it's the perfect moment to buy it.
Prices for used Wii Us are around 200 EUR in my region. I'd say that's not a bargain and makes the idea of a new Switch for an extra 100 bucks way more attractive.
The snark is unnecessary. Of course they exist. Whether they are "dirt cheap" and whether the associated trade-off in quality expectations is worthwhile are entirely legitimate debates.
For example, I saw refurbished Wii U consoles for $200 the other day, and I'd be hesitant to spend $100 or $150 on a device with no warranty. But for $200 it's not crazy to think you might as well go for the Switch at $100 more.