Why was RCB's mankad appeal against LSG turned down by umpire?

RCB pacer Harshal Patel attempted to mankad LSG's Ravi Bishnoi and hit the stumps after initially missing contact. However, the appeal was turned down by umpire Anil Chaudhary. As per an official, the bowler was already four-five steps ahead of the crease and had no intention to deliver the ball. He also stated that Harshal had crossed his last stride.