I think the distinction is in the ability to perceive the risk.
A burning building is a burning building (ok... there's actually a lot that going into assessing the risk posed by a fire in a building, but you get the idea...). A potential confrontation with someone selling cigarettes is an unknown. Odds are, it's not going to be a problem at all. However, there is a small (but non-trivial) chance that it will become a violent encounter (even with fantastic deescalation skills). Given that unpredictability, the safest course of action, it makes sense to have enough manpower on handle to safely deal with a violent encounter.
That being said, the cops in Eric Garner's case did not attempt any deescalation at all (quite the opposite, in fact). The resources on scene were not the issue, the rapid escalation was the issue.
Even at that, it was not the 'chokehold' that killed Eric Garner. It was being placed on his stomach, with his arms behind his back. It's difficult for anyone to breathe in that position, and _very_ difficult for someone of Eric Garner's size. The fight dramatically increased his body's need to get oxygen (and more importantly, get rid of carbon dioxide), and then he was placed in a position that made it all but impossible for his body to do that. We have known for years that this is a dangerous thing to do, yet it happened anyway. Even the EMTs on scene later ignored the risks of his position, and in my opinion, are just as culpable in his death.