Because there's so many PIC, MIP, and PS/2 systems out there running debian?

The war is over. ARM and x86 won.

RISC-V is well on its way to be a challenger to both, with (eventually) full support for Rust.

I'll be happy if it does, but I very much have a "I'll believe it when I see it" view of new archs like RISC-V.