Why aren't "reverse blogs" popular?

They're kind of an evolutionary branch not taken.

The nearest analog that comes to mind is Slashdot's system of taking submissions but having a small number of editors actually making the posts, which often synthesized different articles, so the discussion was about the story more than a specific link.

That might have eventually popularized the kind of "reverse blog" you're talking about, but Blogger/MovableType made it a lot easier and normal to host your own blog, while vote-driven aggregators like Digg and Reddit took out the editorial aspect.

Then we ground everything up into a slurry of "user-generated content" on centralized platforms...

This is like a newspaper or magazine, but small and presumably no money for the writers. Seriously though, pretty neat idea. I think the problem can be getting critical mass of submissions to choose from.

I think a better idea is a "funnel blog", where the community rates articles.

Your feed always consists of current top-rated articles so far PLUS "random" submitted articles for you to rate. Those community ratings cause articles to bubble-up to the top for more users.

Slashdot and reddit kind of implement that on a large scale but it would be great if a ratings funnel was a built-in feature of smaller blogs, podcasts players, etc.

I think of blogs like that as "blogs", not "reverse blogs". They used to be very common, but I suspect that they became less popular as noncommercial blogging itself became less popular.