^ Why? Wii U is dead. It may come to NX tho. 3DS I get,despite the 2D appearance it's probably a hefty game. Some of these retro looking games can't run on retro hardware but need newer stuff to run them.
You're not getting it. Those are real retro games. Mania is a faux one. Made to look retro but it much more demanding than those. A Genesis could never run it. GPUs do not actually do 2D anymore they all do 3D only but games like Sonic Mania give the appearance of 2D when it's really 3D. Things work different. Treachery in Beatdown city looks like an NES games but could never run on a NES. It needs more modern hardware.