That's because the Wii U was poorly marketed, many people though that it was simply an add-on for the Wii or similar, many promises were made like a lot of third party developers working for the console at launch, and look at how far the WiiU is now when it comes to the amount of games.
Compatibility is very important, heck, there was an outrage from Sony fans when the newer PS3 models (Slim & Super Slim) were announced to be non-compatible with PS2 games, although they retained PS1 games compatibility, not only that, if you want to lure in people to buy your console, you need to have a strong amount of games in order to get people interested, specially at Launch, but if Nintendo doesn't provide that, what can you do with a Nintendo Switch other than brag?.
No Game No Life.