These are likely the last leg of inventory Nintendo had from it's warehouses which just recently started opening again. Much easier to ship these to Walmart to clear stock than their site that doesn't have nearly as much traffic.
I agree, these aren't coming back in stock, this is just the last bit of stock Nintendo of America had.
There is no way Nintendo is still wasting manufacturing resources producing 2ds/3ds hardware. These are definitely remaining inventory that probably got delayed/stuck through last holiday, when Nintendo wanted to focus on and move as many Switch consoles as possible.
No sense in making old hardware when the business is focused on selling software on the Switch.
That Ninty is only selling these via Walmart is another signal these are from a final batch. Nintendo is not in the business of selling consoles exclusively.