[BoorishBears]

There's increased development costs on multiple fronts.

Common AAA engines don't support multiple platforms seamlessly, each platform has it's own input devices, asset formats, etc. that need to be supported.

When I worked on a team using the Wii U's Unity3D environment, Wii U builds required a special version of Unity3D, obviously needed to support the specialized form factor of the Wii U's input devices (I'm sure Nintendo has new guidelines on what each game has to support when Joycons are attached and detached). There were even guidelines on how the home button was handled across platforms or how long you could spend loading assets.

Not to mention many large AAA studios are using their own engines (Nintendo had a third tier of development tools reserved for them, that allowed native access and did nothing to support cross platform development) that aren't built to support the Switch without an investment that's greater than on the fairly similar Xbox and PS4.