For better or worse, in Github, random contributors submit whatever they want to, whenever they want to. Most get bent out of shape when their prs aren't mmediately tested and merged by the devs.
Which uses up dev time. A lot of it. (And who really wants to spend days and weeks testing someone else's stuff?)
But they don't want to discourage good contributions.
So...
You prioritize. It's a basic, minimalist, workable, self defense mechanism.
And submissions come in all over the map.
I welcome the recent focus on specifying RCs. It sets priorities and expectations. RC2 is a polite way of saying well look at your contribution. Later.
It's a good thing.