I don't disagree that the market is small, though. But Nintendo does have a chronic problem of under-manufacturing desirable hardware. Like, if you want a SNES Classic (good emulator, fantastic controllers), you'll have to pay 2-3x the original price. Nintendo could do another run of them every year for basically no effort, and they just...don't.
If you mean third party solutions I think there is at least one project that aims to be compatible with various original cartridges but its name eludes me at the moment. [edit] It's Polymega though it doesn't support N64 it does support SNES/Megadrive/NES/TG16 and a number of CD-ROM based consoles.
https://www.kickstarter.com/projects/2134113860/warrior-64-c...
But yeah, Nintendo could have done this years ago had they wanted to.