Historically, porting console games from one to the next isn't always the easiest task since the hardware is so specialized. I think it's been fairly easy for Microsoft because they basically just put out a standard PC every console generation, and their controller design has been pretty much exactly the same since the beginning. But Sony and Nintendo have had some weird hardware. The PS3 was infamously difficult to develop for because it had some wacky architecture under the hood, and we've only recently seen somewhat capable emulation efforts for it.
And Nintendo's in a particularly weird situation where even if it wasn't just the underlying architecture, the consoles all have some kind of "gimmick" where you couldn't really play them on a different system without rethinking the entire game. Like, if you bought a Wii U game digitally, the game was designed around being played on a TV with a secondary resistive touchscreen controller. How would you play that on the Switch, where you only have one screen which may be either on the TV or handheld, and it's capacitive instead of resistive? Nintendo has ported some Wii U games to Switch, but they involved manual work to change how some stuff works. Same with when they port Wii games to it. Super Mario Galaxy was made for a Wii remote and nunchuck, and had a lot of motion control gameplay elements that had to be redesigned to work on Switch.
Historically, porting console games from one to the next isn't always the easiest task since the hardware is so specialized
Yeah, it's tough when the consoles have roughly comparable performance. When they don't it's less so. Amateurs without access to source code got the Dreamcast to run Playstation games better than the Playstation. They got the PSP the run N64 games. They've gotten the Switch to run everything from the Dreamcast down. It's less work than that for internal developers; Nintendo basically made an N64 emulator for the Gamecube as a lark just to offer a free pre-order disc with Wind Waker.
And Nintendo's in a particularly weird situation where even if it wasn't just the underlying architecture, the consoles all have some kind of "gimmick" where you couldn't really play them on a different system without rethinking the entire game. Like, if you bought a Wii U game digitally, the game was designed around being played on a TV with a secondary resistive touchscreen controller. How would you play that on the Switch, where you only have one screen which may be either on the TV or handheld, and it's capacitive instead of resistive? Nintendo has ported some Wii U games to Switch, but they involved manual work to change how some stuff works. Same with when they port Wii games to it. Super Mario Galaxy was made for a Wii remote and nunchuck, and had a lot of motion control gameplay elements that had to be redesigned to work on Switch.