The Debian distribution provides support for numerous processor architectures and it's one of the most prolific in this area. It looks like MIPS support will continue to be offered by the Debian maintainers after the developers get their hand on some new MIPS-powered hardware.
One of the problems for the maintainers in any serious distribution is the lack of access to specific hardware. For example, until the Ubuntu MATE developers got their hands on actual PowerPC hardware, it would have been impossible to provide support for that specific processor.
The same goes for other platforms, and the reason everyone makes distros for X86 processors that everyone has one. There is no fight over who is doing the port for MIPS processors because this hardware is not all that famous, and not many users have this at home, not to mention developers.