Firstly there is no fucking such thing as a incapicitation shot. If you get shot and you LIVE, consider yourself lucky as getting shot anywhere on your body can kill you.
Secondly, whenever a suspect is wielding a deadly weapon and they REFUSE to drop it and surrender, they have forfeited their privilege of attempting a non-lethal resolution. IDGAF if someone is holding a butter knife, as long as they're wielding an object that can apply lethal force easily, it is in the police's best interest to take them down ASAP and as effectively as possible or risk endangering themselves and pedestrians.
Ultimately with police, most scenarios have to be interpreted as a worst case scenario hence the perceived use of excessive force.