Windows CE for Dreamcast ran a custom port of DirectX 5 and subset of Win32 so developers could create a game that supported both desktop Windows and Dreamcast more conveniently.

For games that didn't need to be cross platform, it was still less of a hassle to develop on Windows CE because you got all of the services that having an OS provides you instead of having to write to the bare metal, which is what the Sega SDK required. Many developers chose the Sega SDK anyway because bare metal was what they were used to but IIRC that generation was the last console generation where bare metal was an option for developers.