In Debian, there's no single entity which decides on things. There are rules, and processes.
The relevant documentation is here: https://wiki.debian.org/PortsDocs/New
Also, the rules for becoming an official port is here: https://ftp-master.debian.org/archive-criteria.html
When RISC-V satisfies the relevant criteria, they can become official.
Also, maintaining a port is tremendous amount of work. Debian users only see the tip of the iceberg. There's so much beneath that.