Valve kinda doesn't know what they want their own review system to be. Their response to reviews trying to be meta or funny was to add a new label ("Funny") instead of moderating them to make reviews useful again. It turned a Valve problem into a user problem, which is something Valve is want to do when faced with a problem. (See also: Game sorting in Tags, curation in Greenlight and then Curators, game surfacing in the daily queue, and forum moderation in how developers moderate themselves.) For years, this has worked to undermine what a user review is supposed to be, leading to the system we see before us: one where almost anything goes.
Like, I dunno about y'all, but I look at the review percentage, check recent and top reviews for any red flags on a game (which I could also use the forums for), and that's it. Steam's user reviews aren't helpful on their own, they're only helpful as a wider metric for the state of a game. (which Valve further enforced with their review timeline thing) It's yet another system Valve doesn't want to deal with so it just puts a bandaid on the thing and sets it aside.
And in terms of review bombing, the answer is moderation. As in, review standards that are enforced by Valve themselves. But I doubt Valve is willing going to do that so they might as well give up now. Because you can't put it in developers hands because that will be abused, and expecting anything more from users (like reporting useless reviews when there's already too many of them) is too much to ask.
Valve's continued problem is that they want to turn Steam into a perpetual machine that operates on its own when that's impossible. Their answer of offloading work from themselves has to stop. They have to take control of the platform they've created and own it all.
