it's a weird thing. i personally remember when valve took a far more curatorial stance in what made it through to steam and it led to many unpleasant limitations on what was available to buy, including some pretty savage shut-outs of perfectly good games.
the floodgates are seemingly open, but i'm a big boy now and i'm pretty okay with being the master of my own mispurchase destiny. i can see the issue of having shitgame: repocalypse's name broadcasted without prejudice to millions of cud chewing punters, but i think the key here is transparency and availability of criticism.
it's not talked about much, but i'm finding the steam review system pretty fantastic. you often get a wide spread of surprisingly eloquent and on-point critique right there on the store page - it only takes one scroll of the mouse wheel for any prospective buyer to discover that rekoil is a game nobody should buy in its present state.
such is steam's monopoly, for valve to start a process of stamping every title with their official seal of approval would be akin to censorship of the platform. it shouldn't be for valve to make the road any less dark and full of terrors, just continue implementing tools to help us navigate it.