The problem with LTL's (Less Than Lethal) is that they still have the potential to be lethal, and that police tend to be very inclined to use them in situations where their use isn't actually necessary at the moment they are used. There isn't such a thing as a non-lethal weapon, any use of force has risks.
Also the US is in kind of a difficult situation when it comes to equipping their police force. Due to the massive proliferation of firearms in the country, it is highly variable as to what kind of threat an officer may face. They may face an unarmed person, or they may face a person armed with military grade weapons and hardware.
There are a lot of reasons why most US police now have access to military grade weapons and body armor, such as the
North Hollywood Shootout. I think the proliferation of firearms has also created this feeling in the police of being besieged by the civilian populace, as the police never knows what the heck they may be dealing with when responding to a call.
Throw in latent & systemic racism into the mix, where police tend to view black males as a serious potential threat, even with a total lack of evidence, and police encounters become very dangerous events.
I'm not sure about the Alton Sterling case, but I wonder how they initiated contact. Its not uncommon particularly when dealing with a black male, for the officers to initiate contact aggressively. Often by yelling commands to the person with gun or sometimes taser drawn.
Think how you would react if you were in this situation: your on the street, all of a sudden 1 or more cops approach you, draw their weapons and scream compliance commands at you? How would you react, or would you even be able to react at all? What if they then tased you (which hurts an awful lot, and they disorient), how would you then react then, and do you think you were resisting arrest?
Then take all of that and consider what if you were a black man in this situation, where the same chain of events will probably result in your death.