Open source doesn't mean that it has to accept PRs. It has never meant that the code author's must accept community contributors.
OpenCode has an MIT license, which allows you to copy/fork the code and modify it how you see fit.
Please review the open source initiative's definition of open source: https://opensource.org/osd
I pinged the OC devs to get someone else's PR merged to fix a slop artifact, they did indeed merge external PRs.
Like many popular Ai projects, they get 1000s of slop PRs. They are also working on a v2, so fixes to old code are much less likely to land now.
SQLite famously doesn't accept PRs either, and it's public domain.