Nintendo's New Fit Game (Ring Fit Adventure™)

[Pyro as Bill]

Super Mario Bros. is a pretty singular example, you're probably talking about the most famous video game series in history. You're can't use that as a barometer for everything and NSMB was inexplicably also the first new 2D Mario game actually starring Mario since 1992. So about 14 years in between. 

Most 2D platformers don't do massive business these days. 

Wii Fit U flopped just a few years back, Mario Kart 8 is the best selling game on the Wii U I believe by a large margin, it's just limited by a tiny userbase. Wii U sold about 13 million consoles and MK8 sold like 8.5 million copies, meaning the attach ratio there is insanely high. 

Super Mario Bros. is a pretty singular example - 2D fighting games? Tekken, Virtua Fighter and Soul Calibur (arguably 2.5D) all came and went with massive fanfare. Street Fighter 4 did amazing last gen and Smash and Mortal Kombat and the biggest fighters today.

Most 2D platformers don't do massive business these days. - Are they doing better or worse than the N64/GC days?

So Mario Kart can flop because of userbase but Wii Fit can't?

Eye-Toy came and went, did that mean Kinect couldn't make billions of dollars?

At least be honest with yourself. These games can't succeed again because you don't like them.