How do things like Sated Devourer make it past the PBE? Why are balance updates so slow?

Just started playing again after a long break. One thing that's certain with League is that something is always overpowered. See the phases where entire champions are left in the dust with no play, champs have 95% pick/ban rates, so on.

Now, with everyone saying its as imbalanced as it is, how does an item like Sated Devourer make it past the PBE without getting any nerfs? We know that the balance updates for League are slow anyway, so the least they should be is effective. Currently the only thing it's done is make me remember why I stopped playing in the first place. Victory is decided at the champion select screen. Who has womboes, who has the OP carries. T_T

Riot runs the largest game in the world, I'm certain that a lack of testing data isn't the problem. Even so, things get pushed to live that are insanely imbalanced, and entire matches are decided within the first ten minutes.