Linux doesn't do pull requests. You actually send your patches as an email to a kernel maintainer (different people accept patches for different parts of the codebase) and then they'll review it. They'll pass it up to someone above them, and they'll pass it to someone above them, and eventually it makes its way to Linus.
That's why Linus is famous for angry and aggressive emails. He's not shouting down new developers who have made a simple mistake. He shouts and swears at the people employed below him who failed to properly do quality control and code review.
Currently, you rely on Nvidia to keep the drivers up to date and working with the kernel you use in your OS.
If the drivers aren't upstream, a future kernel can break them. So if you update your OS, it might no longer support your GPU without installing an alternative. Nvidia are responsible for getting this fixed in a timely manner.
If the drivers are upstream, then people aren't allowed to break them when they make changes to the kernel. There should never be a kernel or OS upgrade that causes the drivers to no longer work, the people who made the breaking change are responsible for fixing it before it gets released to you.
But there are massive massive test suites run by hundreds of companies on linux-next. If you email off a stack of patches that breaks something, chances are you'll get emails back telling you which patch had the breaking change in.
Linux doesn't do pull requests. You actually send your patches as an email to a kernel maintainer (different people accept patches for different parts of the codebase) and then they'll review it. They'll pass it up to someone above them, and they'll pass it to someone above them, and eventually it makes its way to Linus.
That's why Linus is famous for angry and aggressive emails. He's not shouting down new developers who have made a simple mistake. He shouts and swears at the people employed below him who failed to properly do quality control and code review.