One, when a target is shooting at you or going crazy because of drugs (and has supernatural strength because of the drugs), there is no reason to try to shoot the offender's legs. In Jacob Blakes's case, it is up to the cops to decide. We, as people sitting behind screens, only get about 30% of detail and info on the current situation. Cops have extreme training in these areas. It was highly likely that Blake was needing more than the minimum two or three shots. I don't know completely why, but we can't make a reasonable judgement based off of one video.
Also. Center mass until there is no more threat.