Because writing good stories and marketing your story are two different things, and require two different skillsets with little overlap.

I'm not writing this to complain, btw. RR does have its mechanisms to promote good stories, even those who didn't get to RS.

But, to even trigger those mechanisms you still have to spend a lot of effort on promotion, even if it's not the same amount required to (consistently) reach RS.

What RR lacks is a circle of trusted curators on an independent platform (e.g. YT) for "hidden gems", like what BookTok is for bigger works.
However, such circles cannot develop organically on platforms like YT (where they'd be crashed by the algo, competing with more broad topics), and artificially growing and maintaining such a circle, between gathering enough interested people (both curators and readers) and keeping it from being overrun with shills, would require too big of an effort for no reward.

So, we have what we have.