This is a bit weird.
It can't because of Switch. When they have 3 more months (Christmas included) to sell it, why take it out of stores?

Perhaps they felt it was damaging their brand to have it sitting there at $299.99 while the PS4/XB1 next to it have deals for cheaper than that with full HDDs. 

I think the answer is, with Switch presentation coming in less than 4 weeks, they don't want to be remembered as the ones that made Wii U :D 
They don't want to jinx it!

I have a better theory...

They don't want to have on the shelves something that would cost most than its successor... ;)

Although, as another person said, why they just don't slash the price? They will lose less money than with the recalling procedure.

Is it better to go and landfill them rather than reduce the price though? I mean this is like saying it's better to throw away a product than admit you made a mistake with the pricing of it originally. It's such a thick headed (as a rumour which has zero evidence other than complete word of mouth rubbish) mindset that if people aren't willing to pay the extortionate price that they put the system at due to their own mistakes then the customer doesn't get to have the remaining systems at a lowered price but instead they would rather sink more cash into the system just to discard them and halt any budget gamers buying a console.

Good idea in a way if it is in the same region of power as the Wii-U and going to cost 2-3x the price if they were to drop the Wii-U down to where people would just impulse buy it.

TBH now though, if you were to buy a full priced Wii-U today (actually more expensive than a ps4/X1) how much buyers remorse would you have over the next weeks/months if you were uneducated as to what is going on with the Wii-U / Switch in the long term. As in if a parent goes in a shop, knows the Wii name, buys the console for the kids, finds out in March it is being trashed completely for the new Nintendo system = one angry mummy!

Now sure if having such an expensive Gamepad was worth it in the end for Nintendo. 4 years later, and how many price drops did it have?

Maybe they need them as replacement units as long as they'll have to support the units already sold to end users.
Or maybe they want to make potential buyers pay for not having bought them before, some sadistic stuff surely devised by Reggie.

Why though?

Isn't it better just to sell the remaining inventory you have?

Nintendo always made some weird policy that some times i just cannot understand.