The AD Meta
Anyone else notice how AD fighters and AD assassins are like a beat up quarter ride outside of a grocery store? No matter how beat up they get, no matter how raggy and destroyed they look, if you put a quarter in (they get a kill or their first item) they still go just as if they were brand new. I partly want to blame itemization for this. AD penetration is so much more cost/slot effective than building hp and armor. So that when later in the game you can afford to build your first penetration item, everything your tanky opponent worked for is just gone.
I can't be the only one who see's this. It's why you see Yasuo, Rengar, Zed, and Riven every game.