Cause Darius suffers from the same problem as all the popular tops (including Elise). They build pure HP and become unstoppable mid game cause their innate damage is ridiculously high. Late game they're unstoppable unless your ADC has a full build.
TBH it doesn't matter which top you ban, ALL of the tops build the same items and do exactly the same thing, there just aren't enough bans to go around. --- Hidetaka Miyazaki, Shinji Mikami Please come back Q_Q