Problem is that it kills momentum for any new Mario game for the next few years when it would much more profitable to just release the new game as it's going to be big enough to carry a holiday season by itself.
NSMBU won't be that, the fact that we're already 8 months in 2018 and we have no concrete information about it shows that it's not going to be the flagship release MK8 was or Pkmn LG or SSBU are going to be.
Mario Maker will very likely be the next 2D Mario game to be released. NSMBU will have no effect on the momentum of a new Mario Maker. If you think Nintendo are done with the Mario Maker concept, they are not. There are a lot of ways they could go with it from here that would be equally or more ambitious than a stand-alone 2D Mario.
On top of that there's an argument to be made that NSMBU is probably not a product good enough for Switch when it failed to make WiiU appealing while NSMBW was basically their biggest title and was partly responsible for Wii's unbelievable end of year 2009 performance. I'm saying NSMBW was popular enough that it pushed hardware sales through the roof while NSMBU got a much more tepid reaction.
New Super Mario Bros. U was the third best selling Wii U game at over 5.5 million and literally everything on the Wii U got a much more tepid response in comparison to their Wii counterparts. The game itself is widely considered the best in the NSMB series quality wise.
We already know that releasing to many NSMB games close to each other is a surefire way to make one of them irrelevant (NSMB2/NSMBU) so a 2008 release for a NSMB port would mean no 2D Mario for 2019.
I don't think anyone is going to buy Switches to get to NSMBU as well.
Captain toad and DKCTF shouldn't be used as examples Captain toad didn't even cross 1M on Switch and DKCTF barely sold more than Metroid Prime 2 on WiiU.
NSMBU is in a different place compared to these 2 games and is after all the 2nd best selling WiiU title.
Maybe no one will rush out to get a Switch because of the port, but the point of these ports is for Nintendo to capitalize on lost sales from the Wii U with a ravenous Switch fan base. Captain Toad
just released, I'm not sure why you were expecting it to be an instant million seller when the original never shipped a million. That said, I bet it will be by the end of the year, easily. Donkey Kong Country: Tropical Freeze sold incredibly well, surpassing the Wii U sales already in its first quarter and since I think you tried to make the random ass comparison to Metroid Prime 2: Echoes... on Gamecube (not Wii U)... it will easily be 2-3 million seller by the end of its run and far surpass Echoes. These ports are meant to fill in and act as high margin profit rakers, Nintendo knows they aren't the main draw to the system.
