It's not really a good comparison to smash characters. If MK8D wasn't ported, we would get a brand new mk on the switch. Now there might not be one for like 5 years on the switch 2. That's a decade of mk8 for people that had it on the wii u. It's fair for people that had a wii u and most games to look at the situation.I can understand the port complaints to a certain degree but I don't think it's quite as simple. Ports such as Mario Kart 8 DX, Tropical Freeze and NSMBUDX serve to 1. extend the lifetime of those games beyond the failure of the Wii U and 2. to let those development teams work on different things. The theories that one game cannot appear on a system just because another is on it seem a bit farfetched and we've seen similar statements over and over again. Why make a 2D Zelda game when you can have 3D Zelda? Why make a 2D Mario when you can have Mario Maker? Nintendo releases tons of games that feel "redundant" to people (especially 2D ones, for some "weird" reason).
In the end, we used to get a new Mario Kart every 3 years for a very long time and I'd argue most didn't approach the level of quality and content found in MK8DX. Other series don't get nearly this many entries. Yabuki worked on three Mario Kart games before he was finally able to do something new. Other teams at EPD don't get that chance at all. That's why I find these complaints a bit backwards. Instead of looking at these ports as a nice little extra, the first impulse is always to think that people are being robbed of something. It's the same weird attitude people have towards Smash characters they don't like.